Boiler types and which suits which home
Combi (combination): instant hot water, no cylinder, no tank. Best for 1–2 bathroom homes with 1–2 occupants. Cheapest install, smallest footprint. System: stored hot water cylinder, no tank. Best for 2–4 bathroom homes with simultaneous demand. Regular (heat-only): cylinder + cold tank in loft. Older system, replaced like-for-like in unrenovated homes. New installs nearly always combi or system. Hydrogen-ready (H2-ready) boilers are available; 100% hydrogen network not yet deployed.
Sizing and efficiency
Heating load: roughly 5–10kW for a 1-bed flat, 12–18kW for a 3-bed terrace, 20–30kW for a 4–5 bed detached. Combi DHW output drives oversizing — 30–35kW typical for a 2-bath family home. Oversizing boilers reduces efficiency by short-cycling — match boiler to load, not to legacy specs. SEDBUK A-rated minimum (legal requirement). Look for ErP A-class space heating efficiency (94%+). Always installed with magnetic system filter (£90–£180 fitted) — extends boiler life dramatically.
Installation scope and gas safety
Standard replacement: drain system, remove old boiler, fit new boiler with new flue, power flush system (1–2 day job, £450–£800), refit gas and water connections, commission and notify Gas Safe Register. Notification triggers building control (handled by Gas Safe engineer — no separate fee for like-for-like). Boiler relocation, fuel change or first install in a property need separate building notice (£250–£450). Always demand the Benchmark log and Gas Safe certificate at completion.
