• Existing heating pipework.

• The number of bathrooms.

• Household hot-water demand.

• Incoming water pressure and flow.

• Available gas, oil or electrical supply.

• Boiler, flue and condensate positions.

• Heating controls and zoning.

• Planned extensions or future alterations.

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APN Boilers helps homeowners find experienced heating professionals who can assess the complete system and recommend an appropriate central heating boiler for the property.

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What Is a Central Heating Boiler?

 

A central heating boiler heats water for distribution around a building.

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The heated water is normally circulated through:

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• Wall-mounted radiators.

• Towel radiators.

• Wet underfloor heating.

• Fan-assisted convectors.

• A domestic hot-water cylinder.

• Separate heating zones.

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Depending on the boiler type, domestic hot water may be:

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• Produced directly when a tap is opened.

• Heated and stored within a separate cylinder.

• Supplied through a traditional cylinder and roof-space tank arrangement.

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The boiler is only one part of the central-heating system. Pipework, radiators, pumps, valves, controls and hot-water storage all affect how effectively the property is heated.

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Types of Central Heating Boiler

 

Domestic central heating boilers generally fall into three main system arrangements:

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• Combi boilers.

• System boilers.

• Regular or heat-only boilers.

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These arrangements are available using different fuels, including gas, oil and LPG. Electric boilers use electricity rather than combustion but can also supply conventional wet central heating.

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Energy Saving Trust identifies combi, system and heat-only boilers as the main boiler arrangements available to UK homeowners.

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Combi Central Heating Boilers

 

A combination or combi boiler provides central heating and domestic hot water from one appliance.

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It heats hot water when a tap or shower is opened, so a separate hot-water cylinder is not normally required.

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Benefits of a Combi Boiler

A combi central heating boiler can provide:

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• Heating and hot water from one appliance.

• No separate airing-cupboard cylinder.

• No traditional cold-water storage tanks.

• A compact installation.

• Hot water on demand.

• More usable storage space.

• A relatively simple heating arrangement.

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Combi boilers can be particularly useful for flats and smaller or medium-sized houses where space is limited. Energy Saving Trust notes that they are often suitable for smaller households but can be less appropriate where several bathrooms require hot water simultaneously or the incoming water pressure is low.

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Checking the Water Supply

The performance of a combi boiler depends on the incoming mains water supply.

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The installer should check:

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• Static water pressure.

• Working water pressure.

• Incoming flow rate.

• Pipe diameter.

• Distance between the boiler and bathrooms.

• Simultaneous hot-water use.

• Shower and bath requirements.

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A high-output combi boiler cannot create more water than the incoming main can deliver.

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Where two or more showers may be used at the same time, a stored hot-water system may provide better performance.

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System Central Heating Boilers

 

A system boiler heats the property and works with a separate hot-water cylinder.

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Many of the principal pumps and heating components are incorporated within the boiler, while hot water is stored for use by baths, showers and taps.

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Benefits of a System Boiler

A system boiler can offer:

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• Stored hot water for larger households.

• Better support for several bathrooms.

• Simultaneous hot-water use.

• Compatibility with modern unvented cylinders.

• Potential integration with solar thermal systems.

• A suitable arrangement for larger family homes.

• Flexibility for future extensions.

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Energy Saving Trust identifies system boilers as particularly suitable for larger households with higher hot-water requirements because stored water can supply several outlets at once.

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The cylinder should be sized around:

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• Number of occupants.

• Number of bathrooms.

• Bath and shower use.

• Simultaneous demand.

• Reheat time.

• Available cupboard space.

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A powerful boiler connected to an undersized cylinder will not provide the expected hot-water performance.

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Regular or Heat-Only Boilers

 

A regular boiler may also be described as:

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• A conventional boiler.

• A traditional boiler.

• A heat-only boiler.

• An open-vent boiler.

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It normally works with a separate hot-water cylinder and may use cold-water storage and feed-and-expansion tanks within the roof space.

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When Is a Regular Boiler Suitable?

A regular central heating boiler may remain appropriate where:

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• The property already has a traditional system.

• Existing pipework is designed for an open-vent arrangement.

• The incoming mains water pressure is limited.

• The property has several bathrooms.

• A substantial quantity of stored hot water is required.

• A like-for-like replacement would reduce disruption.

• Existing tanks and cylinders remain suitable.

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Heat-only boilers generally require more space than combi or system boilers because of the additional tanks. They can nevertheless suit larger homes and properties with lower water pressure.

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Replacing a regular boiler does not automatically mean the property should be converted to a combi system.

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Gas Central Heating Boilers

 

Gas central heating boilers are widely used in homes connected to the mains gas network.

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They are available as:

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• Gas combi boilers.

• Gas system boilers.

• Gas regular boilers.

• Floor-standing boilers.

• Wall-mounted boilers.

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Modern gas boilers are generally condensing appliances, designed to recover more heat from combustion gases than older non-condensing boilers.

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Choosing a Gas Boiler

The installer should assess:

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• Property heat loss.

• Heating output.

• Hot-water demand.

• Gas-pipe capacity.

• Available gas pressure.

• Incoming water flow.

• Boiler location.

• Flue clearances.

• Condensate drainage.

• Existing radiators and controls.

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The required central-heating output may be considerably lower than the boiler output needed to provide fast combi hot water.

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For this reason, the boiler’s minimum output and modulation range should also be considered. A boiler that cannot reduce its heating output sufficiently may repeatedly switch on and off in a smaller or well-insulated property.

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Gas-Pipe Requirements

 

A new gas boiler may require a different fuel flow from the appliance it replaces.

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The Gas Safe engineer should verify that the gas pipe can provide sufficient pressure while the boiler and any other gas appliances are operating.

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Gas-pipe alterations may be necessary where:

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• The existing pipe is undersized.

• The new boiler has a higher gas input.

• The boiler is being relocated.

• The route from the meter is long.

• Other gas appliances have been added.

• The existing installation has excessive pressure loss.

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Any required upgrade should be identified within the quotation.

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Oil Central Heating Boilers

 

Oil central heating boilers are widely used in rural and off-grid properties without access to mains gas.

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Oil boilers are available as:

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• Oil combi boilers.

• Oil system boilers.

• Regular oil boilers.

• Internal boilers.

• External boilers.

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An oil system requires a storage tank and fuel-supply pipe in addition to the boiler.

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Assessing an Oil Heating System

A professional survey should include:

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• The condition and age of the oil tank.

• Tank position and support.

• Delivery access.

• Fuel-supply pipework.

• Isolation valves and filters.

• Fire-valve arrangements.

• Boiler output.

• Flue location.

• Condensate drainage.

• Radiators and heating pipework.

• Hot-water storage.

• Heating controls.

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The existing oil tank does not automatically need replacing when a new boiler is installed, but it should be inspected and confirmed as safe and suitable.

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Oil Boiler Installation and Certification

Heating installations must comply with the applicable Building Regulations. Appropriately registered OFTEC installers can self-certify qualifying work in England and Wales, avoiding the need for a separate Building Control inspection where the installation falls within the competent-person scheme.

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Homeowners should retain the compliance certificate, commissioning documents and boiler warranty information with the property records.

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Electric Central Heating Boilers

 

An electric central heating boiler uses electrical resistance elements to heat water for circulation through radiators or wet underfloor heating.

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It does not require:

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• A mains gas supply.

• An oil or LPG tank.

• A combustion flue.

• On-site fuel deliveries.

• Combustion ventilation.

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Electric boilers may be useful for:

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• Flats and apartments.

• Smaller homes.

• Properties without gas.

• Internal boiler locations.

• Buildings where a compliant flue cannot be installed.

• Extensions, annexes and converted outbuildings.

• Existing wet central-heating systems requiring a non-combustion heat source.

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Electric boilers heat water before distributing it through radiators or underfloor-heating pipes. Some systems also use substantial hot-water or thermal storage and may be paired with electricity tariffs offering lower prices during particular periods.

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Electric Boiler and Hot-Water Arrangements

 

An electric boiler may provide central heating only.

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Domestic hot water may be supplied through:

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• A separate direct electric cylinder.

• An indirect cylinder heated by the boiler.

• A combined electric boiler-and-cylinder package.

• Immersion heaters.

• A heat battery.

• Separate point-of-use water heaters.

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Products described as electric combi boilers do not always operate like gas combi boilers.

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Many package systems contain both an electric heating boiler and a stored hot-water cylinder. The boiler and hot-water arrangement should therefore be checked carefully before a product is selected.

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Checking the Electrical Supply

 

Electric boilers can create a substantial demand on the electrical installation.

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The survey should consider:

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• Incoming supply capacity.

• Main fuse rating.

• Consumer-unit capacity.

• Dedicated circuits.

• Required cable sizes.

• Protective devices.

• Local isolation.

• Earthing and bonding.

• Existing high-demand equipment.

• Electric vehicle charging.

• Immersion heaters.

• Single-phase or three-phase availability.

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A competent electrician should confirm the electrical requirements before the boiler is ordered.

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Standard-rate electric heating can have high running costs, particularly when used to heat an entire poorly insulated home. Energy Saving Trust advises that electric heating may be more practical in smaller or highly insulated properties and that tariffs offering cheaper off-peak periods can influence the result.

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LPG Central Heating Boilers

 

LPG boilers operate in a similar way to mains-gas boilers but use liquid petroleum gas stored in a bulk tank or cylinders.

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They may suit:

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• Rural properties.

• Park homes.

• Holiday accommodation.

• Off-grid houses.

• Properties where oil storage is impractical.

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An LPG installation should include an assessment of:

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• Tank or cylinder storage.

• Regulators.

• Fuel pipework.

• Delivery access.

• Boiler suitability for LPG.

• Flue position.

• Condensate drainage.

• Heating and hot-water demand.

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The engineer must be Gas Safe registered and qualified for the relevant LPG work. A qualification for mains natural gas does not automatically cover all LPG installations.

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Biomass Central Heating Boilers

 

Biomass boilers burn wood pellets, logs or wood chips to heat water for a wet central-heating system.

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A complete installation may require:

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• A large boiler.

• Fuel storage.

• Automatic fuel-feed equipment.

• A thermal store.

• A hot-water cylinder.

• A chimney or insulated flue.

• Ash removal.

• Delivery access.

• Regular cleaning and maintenance.

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Biomass central heating can suit larger rural properties with suitable space and a dependable fuel supply, but it is generally less practical for smaller urban homes.

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New Central Heating Boiler

 

Installing a new central heating boiler provides an opportunity to review the entire heating system.

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The project should not automatically be treated as a straightforward appliance swap.

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The existing boiler may have been:

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• Incorrectly sized.

• Installed before the property was extended.

• Selected for a previous household’s needs.

• Connected to outdated controls.

• Serving incorrectly sized radiators.

• Operating through restricted pipework.

• Connected to an unsuitable cylinder.

• Working with contaminated system water.

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A heating-system survey should establish what the property currently needs rather than repeating an old specification.

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Calculating the Required Boiler Output

 

Boiler output should not be selected from bedroom numbers alone.

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A proper assessment should consider:

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• Floor area.

• Wall, roof and floor construction.

• Insulation levels.

• Window sizes and performance.

• Ceiling heights.

• Exposed walls.

• Air leakage.

• Required room temperatures.

• Local winter conditions.

• Radiator outputs.

• Underfloor-heating circuits.

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Two similarly sized properties can have very different heating requirements.

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For combi boilers, space-heating demand and domestic hot-water demand should be assessed separately. The output required for instantaneous hot water may be greater than that needed by the radiators.

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Central-Heating Pipework

 

Heating pipework must carry sufficient water to every radiator or underfloor-heating zone.

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The installer should inspect:

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• Main flow and return pipes.

• Branch pipe sizes.

• Microbore sections.

• Long pipe runs.

• Circulation pumps.

• Zone valves.

• Bypasses.

• Air vents.

• Expansion arrangements.

• Signs of leakage.

• Previous alterations.

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A new boiler cannot correct an inherently restricted or badly arranged pipework system.

 

Where a property has been repeatedly extended, additional radiators may have been connected without checking whether the original pipes can carry the increased flow.

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Radiator Sizing

 

Radiators should be large enough to replace the heat lost from each room.

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The survey should assess:

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• Radiator dimensions.

• Single-, double- or triple-panel construction.

• Position within the room.

• Water temperatures.

• Room heat loss.

• Thermostatic valves.

• Air circulation around the radiator.

• Decorative covers or obstructions.

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A larger boiler will not compensate for an undersized radiator.

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Where lower heating-water temperatures are proposed, some radiators may need to be enlarged or replaced.

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Underfloor Heating

 

Wet underfloor heating can be supplied by gas, oil, LPG, electric and biomass boilers.

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The system normally operates at a lower water temperature than conventional radiators and may require:

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• A mixing valve.

• A manifold.

• Separate pumps.

• Individual room controls.

• Flow meters.

• Actuators.

• Separate heating zones.

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The boiler and controls should be designed to serve the different temperature requirements of radiators and underfloor heating.

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Heating-System Cleaning

 

Old central-heating systems may contain:

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• Corrosion products.

• Magnetite.

• Sludge.

• Scale.

• Debris.

• Chemical contamination.

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These deposits can:

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• Restrict circulation.

• Cause cold radiator areas.

• Damage pumps.

• Block boiler waterways.

• Create noise.

• Reduce heating performance.

• Affect the boiler warranty.

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The installer should assess the water condition and recommend an appropriate cleaning process.

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The completed system may require:

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• Chemical inhibitor.

• Magnetic filtration.

• Radiator balancing.

• Replacement valves.

• Improved air separation.

• Further investigation of persistent circulation faults.

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Central-Heating Controls

 

Modern heating controls can improve comfort and reduce unnecessary energy use.

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Possible controls include:

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• Programmable room thermostats.

• Smart thermostats.

• Thermostatic radiator valves.

• Separate upstairs and downstairs zones.

• Independent hot-water timing.

• Cylinder thermostats.

• Weather compensation.

• Load compensation.

• Individual room controls.

• App-based heating management.

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Control requirements vary according to the boiler arrangement. Combi boilers generally need central-heating control, while system and regular boilers require separate control of heating and stored hot water.

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Controls should be selected as part of the system design rather than treated as an optional accessory after the boiler has been ordered.

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Boiler Flow Temperature

 

The boiler flow temperature is the temperature of the water leaving the appliance and travelling towards the radiators.

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Modern condensing boilers generally operate more efficiently when the returning heating water is cooler, provided the radiators can still heat the property adequately.

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The appropriate temperature depends on:

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• Outdoor conditions.

• Property heat loss.

• Radiator sizes.

• Heating hours.

• Desired indoor temperature.

• Whether a hot-water cylinder is connected.

• The type of boiler and controls.

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Combi boilers normally allow the radiator temperature to be adjusted independently from domestic hot water. A conventional boiler that also heats a cylinder must maintain an appropriate stored-water temperature.

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Homeowners should avoid applying a generic setting without understanding their system.

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Boiler Location

 

A new boiler does not necessarily have to remain in the same position as the old appliance.

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Possible locations include:

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• Kitchen cupboards.

• Utility rooms.

• Garages.

• Airing cupboards.

• Loft spaces designed for boiler access.

• Plant rooms.

• External weatherproof enclosures for suitable oil boilers.

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The chosen location should consider:

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• Access for installation.

• Servicing clearances.

• Flue arrangements.

• Condensate drainage.

• Fuel or electrical supplies.

• Heating-pipe routes.

• Noise.

• Frost protection.

• Safe access for future repairs.

• Manufacturer requirements.

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Relocating a boiler may improve the use of space but will usually increase installation cost and disruption.

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Flue and Condensate Requirements

 

Gas, oil and LPG condensing boilers require both a combustion flue and condensate disposal.

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The flue position should be considered in relation to:

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• Windows and doors.

• Air vents.

• Boundaries.

• Neighbouring properties.

• Roofs and eaves.

• Extensions.

• Passageways.

• External seating areas.

• Manufacturer clearances.

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Condensate may be discharged to:

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• An internal waste pipe.

• A suitable trapped drain connection.

• An external condensate route.

• A purpose-designed soakaway.

• A condensate pump where gravity drainage is unavailable.

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These requirements should be assessed before the boiler location is agreed.

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Central Heating Boiler Replacement Cost

 

The cost of installing a new central heating boiler will depend on the complete scope of work rather than the appliance alone.

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Price may be affected by:

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• Boiler fuel and type.

• Boiler manufacturer.

• Required output.

• Warranty period.

• Boiler relocation.

• Flue alterations.

• Condensate drainage.

• Gas-, oil- or electrical-supply upgrades.

• Hot-water-cylinder replacement.

• Removal of tanks.

• Radiator or pipework alterations.

• Heating controls.

• System cleaning.

• Electrical work.

• Scaffolding.

• Making good.

• Certification.

• Waste disposal.

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A low headline price may cover only a basic boiler swap.

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Homeowners should compare detailed quotations that clearly identify the boiler, controls, system work, certification and exclusions.

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Gas Safe Registration

 

All gas central-heating boiler work must be completed by an appropriately qualified Gas Safe registered engineer.

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Homeowners should check:

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• The business’s registration.

• The individual engineer’s ID card.

• The categories of work listed.

• That the engineer is qualified for boilers.

• Whether LPG qualifications are required.

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Following a qualifying gas-boiler installation, the work must be notified and the homeowner should receive a Building Regulations Compliance Certificate. Gas Safe Register advises that the certificate belongs to the property and should be retained for a future sale or remortgage.

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Oil Boiler Competence

 

Oil central-heating work should be completed by a professional with appropriate oil-heating competence.

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An OFTEC-registered technician can provide:

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• Boiler installation.

• Oil-tank assessment.

• Fuel-line work.

• Flue advice.

• Commissioning.

• Building Regulations notification where covered by registration.

• Servicing and maintenance.

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Building Regulations apply to heating-equipment installations, and competent-person registration allows qualifying work to be self-certified in the regions covered by the scheme.

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Building Regulations and Certification

 

A new central heating boiler must comply with the applicable Building Regulations.

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Relevant areas can include:

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• Energy efficiency.

• Combustion appliances.

• Flues and ventilation.

• Hot-water storage.

• Electrical safety.

• Carbon monoxide protection.

• Fire stopping.

• Fuel storage.

• Heating controls.

• Commissioning.

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The installer should provide the appropriate documents, which may include:

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• Building Regulations Compliance Certificate.

• Boiler commissioning record.

• Electrical certificate.

• Unvented-cylinder certificate.

• Manufacturer warranty.

• Heating-control instructions.

• System-treatment details.

• Service requirements.

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These documents should be retained with the property records.

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Central Heating Boiler or Heat Pump?

 

A heat pump may be worth considering before installing another gas, oil or LPG boiler.

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A heat pump can supply a wet central-heating system but normally operates differently from a traditional boiler.

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The project may require:

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• A room-by-room heat-loss calculation.

• Larger radiators.

• A hot-water cylinder.

• Pipework alterations.

• External equipment.

• Electrical upgrades.

• Improved insulation.

• Different controls.

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The Boiler Upgrade Scheme currently provides support for eligible low-carbon heating installations in England and Wales. It does not fund a conventional boiler replacement, but eligible homeowners may receive support towards a qualifying heat pump or biomass boiler.

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The decision should be based on the property, installation cost, running-cost expectations, disruption and the homeowner’s long-term plans.

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What Should a Central Heating Boiler Quotation Include?

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A detailed quotation should identify:

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• Boiler manufacturer and model.

• Boiler fuel.

• Combi, system or regular arrangement.

• Heating output.

• Hot-water performance.

• Boiler location.

• Manufacturer warranty.

• Flue and condensate arrangements.

• Fuel- or electrical-supply alterations.

• Hot-water-cylinder work.

• Heating controls.

• System cleaning and treatment.

• Magnetic filter.

• Radiator and pipework alterations.

• Removal of old equipment.

• Commissioning.

• Building Regulations notification.

• Making good.

• Waste disposal.

• VAT.

• Exclusions and provisional costs.

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The installer should explain why the boiler has been selected and identify any existing-system defects that could limit its performance.

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Find a Central Heating Boiler Installer Through APN Boilers

 

APN Boilers brings together experienced heating professionals serving homeowners across the UK.

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A successful central heating boiler installation should provide more than a replacement appliance. It should include:

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• The correct fuel and boiler type.

• An output matched to the property.

• Suitable heating pipework.

• Correctly sized radiators.

• Reliable hot-water performance.

• Modern heating controls.

• Clean and balanced heating circuits.

• Safe flue, fuel or electrical arrangements.

• Professional commissioning.

• Building Regulations certification.

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Whether you are considering gas central heating boilers, oil central heating boilers or an electric central heating boiler, the complete property and heating system should be assessed before the appliance is selected.

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Tell APN Boilers about your property, existing boiler, number of bathrooms and heating requirements. We will help you find an appropriate local professional to advise on and install your new central heating boiler.

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