Electrics and gas
Where a report pairs an indirect cylinder with the immersion heater, what stays open about a thermostat the survey did not turn?
What stays open is whether the thermostat works, because the survey did not turn it. An indirect cylinder is heated by the boiler through a coil, and the immersion heater is the electric backup in the same vessel. Pairing them names the arrangement. It does not show that the thermostat switches the immersion, that the element heats, or that the boiler coil is clear of scale. The survey has not made those tests. The cylinder and the heater were identified. The control was left untried.
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?
The thermostat on an immersion is a small control, often under a cover on the heater head. Turning it is a simple check, and this visit did not do it, so you do not know if it works. The indirect coil is a further unknown: scale can sit on it without showing on the outside of the cylinder. The surveyor sees the cylinder and the immersion. They do not see inside the vessel, and they did not operate the stat. Identification stops at the case.
Ask an electrician to test the immersion and its thermostat, and a heating engineer to consider the indirect coil. The home survey has done neither. Tell the solicitor the thermostat was not turned, so hot water from the immersion is unproved. If the boiler is gas, keep appliance work with a Gas Safe registered engineer. Do not switch the immersion on as your own experiment and call that a test of the wiring. The survey has not decided the heater is faulty, and it has not cleared it.
What should you ask your surveyor?
- Where is the thermostat, and was the cover left on?
- Did you see a separate switch for the immersion, or only the cylinder?
- Was any scale, weep or overheating mark visible on the heater head?
What are the typical next steps?
- Keep the indirect cylinder, the immersion and the unturned thermostat apart.
- Ask an electrician to test the immersion and its thermostat.
- Tell the solicitor the survey did not prove the electric backup.
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
Does an indirect cylinder work without the immersion?
It can, because the boiler coil is the main heat source and the immersion is the backup. The survey paired the two and did not turn the thermostat, so it has not tested either path. It has not decided the coil is clear, and it has not decided the element works. Both routes stay open until an engineer and an electrician look at them.
Is a warm cylinder proof the thermostat is set correctly?
No. A warm case can mean the boiler has heated the store, not that the immersion thermostat was tested. The survey did not turn that control. Warmth on the day is not a setting and not an electrical test. Ask an electrician if you need the immersion checked. The temperature of the metal is not that check.