Electrics and gas
A back boiler is still piped to radiators and the seller says it is unused. What isolation of that boiler was not proved?
The isolation of the back boiler was not proved. It is still piped to the radiators, and the seller says it is unused. Piping that is still connected is what the survey could see. A seller's word that the boiler is unused does not show a capped gas supply, a disconnected flow and return, or a valve left shut and proved. The survey has not tested the gas and has not demonstrated isolation. Unused, in this note, is an unverified claim.
Last reviewed 24 October 2026. Written for buyers in England and Wales unless this answer says otherwise. No named surveyor has signed this page. It is general guidance, not a report on your house, and not legal advice.
What is the fuller explanation?
A back boiler sits behind a fire and heats water or radiators through pipes. If those pipes are still connected, the appliance is still plumbed into the heating, whatever the seller believes about how often it is lit. Isolation would be something you can see or that an engineer can confirm: gas capped off, pipes blanked, or a written record of making it safe. None of that was proved on this visit.
Ask a Gas Safe registered engineer to confirm whether the back boiler is isolated from the gas and from the radiator circuit. Tell the solicitor the pipes are still connected and the seller's unused claim was not proved. Do not delete the boiler from the fittings enquiries on the strength of that claim. Keep any later disconnection certificate separate from this visual note.
What should you ask your surveyor?
- Are the flow and return pipes to the back boiler still connected?
- What isolation, if any, could you actually see?
- Did the seller's unused claim get checked against the gas supply?
What are the typical next steps?
- Ask a Gas Safe engineer whether the back boiler is isolated from gas and radiators.
- Tell the solicitor the pipes are still connected and the unused claim was not proved.
- Keep any later disconnection certificate separate from this note.
Costs vary with the building and with who you instruct. Where this page does not cite a published figure, ask the surveyor, a relevant specialist, or your solicitor for a written quote. Do not treat a forum average as the price.
Also asked about this
If the radiators are cold, is the back boiler isolated?
No. Cold radiators on one afternoon do not show the boiler is isolated. They may simply be off. The pipes are still there, the survey did not test the gas, and the seller's unused comment remains unproved. Temperature is not a cap on the supply.
Does the fittings form prove the gas to that boiler is capped?
No. A sentence on a fittings form is the seller's account. It does not prove the gas is capped or the pipes are disconnected. The survey saw the back boiler still piped to the radiators and did not test that claim. Ask the engineer, not the form, for isolation.