Consumer watchdog Which? has found that independent heating engineers are much cheaper than British Gas for boiler replacement jobs.
The investigation looked was sparked after several Which? members highlighted wide gaps between British Gas quotes and other quotes for boiler replacements and services.
The consumer group compared British Gas quotes against those from independent central heating engineers on its recommendations website.
British Gas quoted £3,997 to replace a 12-year-old combination boiler with a new Vaillant ecoTEC pro 28 in a one-bedroomed flat in London. For the same work, independent engineers quoted £2,000 and £2,300.
British Gas also quoted £5,106 for a new boiler in a five-bedroom house in Nottingham. However, two independent engineers priced the work at £2,485 and £2,888.
And a Which? member in Manchester said that British Gas quoted £3,457 to replace a heat-only boiler with a modern condensing equivalent, while local contractors asked for £1,700 and £1,940.