Heat only boiler
Plain English. Practical detail. UK context.
A heat-only boiler, often called a regular or conventional boiler, supplies heat to a suitable external heating and hot-water arrangement. The name distinguishes it from a combi, which produces domestic hot water on demand. It does not, by itself, specify every pump, tank, cylinder or pressure arrangement in the home.
Safety: gas work must only be done by a Gas Safe registered engineer who is qualified for that type of appliance. Check their ID card or the Gas Safe Register. If you smell gas, leave the property and call the gas emergency number: 0800 111 999 in Great Britain or 0800 002 001 in Northern Ireland.
Last reviewed: (editorial review against the public sources listed below).
When the arrangement may suit a home
A property with a suitable retained cylinder and associated components may use a heat-only boiler. Energy Saving Trust describes common conventional systems with loft storage tanks, but the actual installation must be identified rather than assumed from the boiler label. Hot-water demand, incoming supply, available space and existing condition all affect replacement options. A household using several outlets has different requirements from a small flat. Ask the installer to compare complete system arrangements rather than judge solely by appliance size, a photograph or a promise that one type is always more efficient.
The boiler is only one component
External pumps, controls, expansion provision and stored hot-water equipment must operate together. A cylinder fault, poor water distribution or an inappropriate control interaction can resemble a boiler problem. Trainees should learn the actual schematic and identify where design responsibilities sit. Replacing the heat source does not automatically make retained components suitable. Maintenance access, safe operation and future replacement need planning, particularly when tanks or cylinders are enclosed by later building work. Avoid removing an apparently redundant component until a competent person confirms its purpose in the system.
Safety, energy and relevant competence
Gas-fired work requires appropriate Gas Safe registration and relevant competence. Oil and other systems have their own requirements. England's Approved Documents L and G address relevant energy and hot-water safety matters, with separate national guidance elsewhere. Applicable editions and transitions need checking for the actual project. A sealed or unvented component introduces particular design and safety considerations; the words heat only do not authorise a simple conversion. Follow appliance and system instructions and obtain the appropriate commissioning and compliance records rather than treat the boiler's successful first firing as the full handover.
A replacement brief with useful boundaries
Agree whether the quote covers the appliance alone or also pumps, controls, cylinder, treatment, pipe alterations and disposal. Ask why the proposed output matches the property's needs. Retain operating instructions and ask for separate demonstrations of heating and hot water. No specific installed cost is inferred from a general replacement-boiler average because this configuration and scope can differ substantially. For tradespeople, record retained-system limitations and clarify necessary further work before ordering. A clear recommendation compares options and responsibilities without inventing savings or promising that a new heat source resolves every existing comfort issue.
Frequently asked questions
Is heat only the same as combi?
No. A heat-only boiler uses a suitable external arrangement for stored domestic hot water rather than functioning as an instantaneous combi.
Does the label prove the home has a particular tank layout?
No. Identify the actual system and appliance requirements before proposing changes or replacements.
Sources and further reading
Public sources and further reading. Sources checked: 8 November 2026. Consult the original for details and later changes.