Back boiler removal: what is involved

What a back boiler is

A back boiler is a small boiler built into the fireplace, behind a gas fire. The fire warms the room. The boiler behind it heats water for the radiators and usually a hot water cylinder in an airing cupboard upstairs. Both share the chimney as their flue.

They were a common way to add central heating to houses that already had a chimney breast, without finding a new place for a boiler. In north London you still find them in older terraces and in some council and housing association flats.

Why Tottenham and Wood Green homes still have them

Tottenham and Wood Green have a lot of Victorian and Edwardian terraces. Noel Park alone is a planned estate of about 2,000 terraced homes built by the Artizans company from around 1881 (Haringey conservation appraisal). Those houses were built with fireplaces in most rooms, which made a back boiler an obvious choice when central heating arrived.

Haringey also rents a lot. At the 2021 Census, 35.6% of households rented privately and 25.2% from a social landlord (ONS). Landlords tend to replace back boilers when they fail a safety check or when parts can no longer be found.

Common reasons to remove one

• The engineer has classed it At Risk or Immediately Dangerous on a safety check
• Spare parts are no longer available for the model
• The chimney no longer draws properly, so the flue tests fail
• You want the fireplace back as a feature, or the room for something else
• A wider refurbishment is moving the heating to a modern boiler

Gas Safe’s warning label guidance explains the unsafe categories. Our post on what it means when a gas engineer turns off your boiler covers your choices if that has happened.

The removal, step by step

Step	What happens	Notes
Survey	Engineer looks at the fire, boiler, flue, cylinder and pipe runs	Also where a new boiler could go and how it would flue
Isolate	Gas is turned off; electrics to the boiler controls isolated	Your heating and hot water are off from here
Drain	The heating system is drained down	Old systems can hold a lot of sludge
Disconnect	Gas and water pipes are disconnected from the unit	Pipes are capped or rerouted
Remove	Fire and back boiler are lifted out of the opening	Heavy and dusty work
Cap and test	The gas supply is capped and the installation tested for tightness	Required before gas is restored to other appliances
Flue	The chimney opening is left safe, with ventilation as needed	Depends on what you want to do with the fireplace

An engineer should also look out for materials that may contain asbestos. Older fireplaces and appliance parts in buildings from before 2000 can include it. If it is suspected, work stops until it has been checked.

The new boiler

Removing a back boiler is really the first half of a boiler replacement. The second half is choosing and fitting the new one. The main choices are:

• A combi boiler. Heats water on demand, so the hot water cylinder and loft tanks can often go. Suits smaller homes and flats.
• A system or regular boiler. Keeps a hot water cylinder. Suits larger houses with more than one bathroom.

Our guide to combi or system boiler for a London flat or terrace goes through the trade offs.

The new boiler cannot use the old chimney in the same way. It will need its own flue, usually through an outside wall or roof, and a condensate pipe to a drain. Rules that apply in England include:

• Boiler Plus: new gas boilers must be at least 92% ErP, with a timer and room thermostat, and a new combi needs one extra efficiency measure.
• Building Regulations notification: the installer must notify the local authority within 30 days, and you then receive a Building Regulations Compliance Certificate (Gas Safe).
• Approved Document J: a carbon monoxide alarm is required when a new fixed combustion appliance is installed.

Water treatment on an old system

A back boiler system has often run for decades. The radiators and pipes can be full of sludge, and Tottenham’s water is hard. Thames Water’s Tottenham South zone averaged 273 mg/l calcium carbonate in 2025 (Thames Water report), which is hard on Thames Water’s own scale.

Guidance in BS 7593 calls for the system to be cleaned, an inhibitor added and a filter fitted when a new boiler goes in, with a scale reducer where hardness is over 200 ppm. Putting a new boiler on dirty old pipework is a common cause of early faults.

Landlords

If the property is let, the back boiler and fire are on your landlord gas safety certificate until they are removed. If the fire is in a room now used as a bedroom, HSE’s rule on gas fires in bedrooms since 1998 may already apply. After the work, update your records so the next check lists the new boiler, and make sure the room with it has a CO alarm.

Getting a price

London Gas Engineers quotes back boiler removal and replacement after a survey, because the cost depends on the new boiler type, the flue route, the cylinder and the state of the pipework. Our gas fire servicing and removal and boiler installation pages explain both halves of the job.