Electrics and gas
A heat-pump cylinder and an old vented tank are both still plumbed in the cupboard. Which one has the survey not proved is in use?
Not which of them is actually in use. A heat-pump cylinder and an old vented tank are both still plumbed in the cupboard, and the survey has not proved which one supplies the taps. It can record two vessels and the pipes it could see. It has not followed every valve, run the system as a test, or shown that one is redundant. Both being connected is not the same as both being live, or as one having been isolated. Ask a heating engineer which cylinder is in service before you assume the old tank is only a spare.
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 change of heating often leaves the old vented cylinder in the cupboard beside the new heat-pump cylinder. Pipes on both can look connected when one set is valved off, capped badly, or still in circuit. A visual survey sees the tanks, the valves in view and any vent or tundish. It does not operate the system long enough to prove which vessel heats, and it does not drain anything. Presence of two plumbed cylinders is not a diagram of the live circuit.
Ask a heating engineer to say which cylinder feeds the outlets, which valves are open, and whether the old tank is isolated or still on the system. Do not shut valves on a viewing to find out. If the seller says the old tank is redundant, put that in writing and let the engineer check it against the pipework. Keep the survey as the record that both were still plumbed. It is not a finding that the heat-pump cylinder has replaced the other in fact.
What should you ask your surveyor?
- Which pipes on each cylinder were visibly connected, and which valves were shut?
- Did you see a vent pipe on the old tank as well as a sealed heat-pump cylinder?
- Could you tell from the cupboard which one was warm, or was that not tested?
What are the typical next steps?
- Do not assume which cylinder is in use from the fact both are plumbed.
- Ask a heating engineer to trace which vessel feeds the taps.
- Do not close valves on a viewing to test the point.
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 heat-pump cylinder is new, is the old tank definitely dead?
No. New and old can both still be plumbed in. The survey has not proved the old vented tank is isolated or that the new one is the only one in use.
Can you drain the old tank on a second viewing?
No. Do not drain it. Whether it is spare or still in circuit is for a heating engineer to confirm with the seller's agreement.