Boiler replacement FAQ

Like-for-like combi swap £1,800-£3,500. System boiler £2,000-£4,000. Regular boiler £2,000-£4,500. Back-boiler conversion £2,500-£5,000. See /by-type for type-specific deep dives.

£2,500-£5,000 all-in. The highest UK domestic replacement cost band because of four extra components: old unit decommission, pipework rerouting, new external flue, and fire surround removal + wall make-good. See /by-type/back-boiler.

Boiler unit, installation labour, flue and fittings, magnetic system filter, powerflush, system inhibitor, Building Control notification via Gas Safe Competent Persons Scheme. Some installers include smart thermostat under Boiler Plus 2018. See /installation for the full handover paperwork list.

Like-for-like combi: 6-8 hours, done in a day. Boiler type change: 1.5-2 days. Back-boiler conversion: 2-3 days.

Yes - legally required under the Gas Safety (Installation and Use) Regulations 1998. Verify at gassaferegister.co.uk.

Requires all new gas combis in England (since April 2018) to include one additional energy-saving measure: smart thermostat with weather compensation, flue gas heat recovery, or weather compensation. Most installers fit a smart thermostat by default.

Almost never - permitted development under the standard rules. Exceptions: listed buildings, conservation areas with visible flue location, and properties with specific planning conditions.

There is no free, independent reliability ranking we can cite with figures. Compare what each maker publishes instead: warranty length and the conditions behind it. See /by-brand.

It depends on the model and on conditions. Ideal Vogue Max up to 12 years and Logic Max 10; Worcester Bosch Greenstar 8000 Life up to 12 with an accredited installer; Vaillant ecoTEC plus 5 years, up to 10 with the Advance kit; Baxi 800 10 years and 600 7; Viessmann Vitodens 7 years on registration, 10 or 12 as paid extensions. Register within 30 days.

Only in narrow cases. ECO4 (an obligation on energy suppliers, administered by Ofgem, running until 31 December 2026) for households on qualifying benefits in an EPC D-G home (E-G if privately rented); a working-but-broken efficient boiler is only replaced if it cannot be economically repaired. The Boiler Upgrade Scheme gives £7,500 for heat pumps, not gas boilers. See /grants.

Some installers (BOXT, Heatable, BoilerCentral) offer 0% finance with no deposit on approved credit. Others require 10-25% deposit. See /finance for the full comparison.

Often, but check what it is first. Boilers installed before April 2005 are usually non-condensing; for a G-rated boiler, the Energy Saving Trust puts the annual saving from replacing a G-rated gas boiler with an A-rated one, with full controls, at £170 for a mid-floor flat to £500 for a detached house (£350 for a semi), at July 2026 fuel prices. A 15-year-old condensing boiler saves less. See /repair-or-replace.

Worth modelling, but rarely the right answer today unless the property is already well-insulated to EPC C+ and you have room for an outdoor unit. Heat pump installed cost £8,000-£14,000 (minus £7,500 BUS grant). See /vs-heat-pump.