Boiler replacement FAQ

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

GBP 2,500-GBP 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.

Worcester Bosch tops Which? Best Buy and installer recommendation surveys, with Vaillant a close second. Ideal Logic Max wins on value-for-money in 2026 ratings. See /by-brand for full comparison.

5-12 years depending on brand and model. Worcester Bosch Greenstar 8000 Life up to 12 years (via Worcester Trade Accredited Installer). Vaillant ecoTEC Plus up to 10 years (Advance Guarantee). Ideal Vogue Max up to 12 years. Always register within 30 days.

Yes if eligible. ECO4 (free or subsidised boiler for households on qualifying benefits with EPC D-G) or Boiler Upgrade Scheme (GBP 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.

Usually yes. A 15-year-old boiler runs at 70-82% efficiency vs 92-94% for a modern A-rated combi. Energy Saving Trust estimates GBP 200-GBP 580 annual gas saving from upgrading, with cumulative 12-year savings often exceeding the install cost. 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 GBP 8,000-GBP 14,000 (minus GBP 7,500 BUS grant). See /vs-heat-pump.