Electrics and gas
The house has both a combi boiler and a hot-water cylinder. Which one is live?
The survey cannot tell which one is live. Both can be plumbed, one can be abandoned, or each can serve a different tap, and the visit did not trace the pipework or test the gas. HSE expects a Gas Safe registered engineer to do gas work, so seeing two appliances is not knowing which one heats the water.
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?
Combinations like this appear when a combi was fitted and the old cylinder was left, or when a cylinder still serves a bathroom and the combi serves the kitchen. The surveyor sees boxes, pipes and valves. They do not drain systems to see which valve is shut, and they do not decide that the cylinder is scrap. An immersion on the cylinder may still be the heat source. A gas boiler may still be. Neither was proved by standing in the airing cupboard. Do not turn valves to find out on a viewing.
Ask the seller, in writing, which appliance they use for hot water and for heating, and ask for service papers for whatever is gas. An owner-occupier is not obliged to produce a landlord gas safety record merely because two appliances are confusing. If you need to know the live one before exchange, a heating engineer and, for the gas side, a Gas Safe engineer can trace it. Their visit is not included in the survey. Do not remove the cylinder in your head and deduct a replacement you have not scoped. Redundant kit is only redundant once someone has shown you it is disconnected.
What should you ask your surveyor?
- Did you see both a combi and a cylinder, and any valves that looked shut?
- Did you trace which one feeds the taps? If not, say so.
- Was any appliance tested?
What are the typical next steps?
- Ask the seller which unit they actually use.
- Do not disconnect either as a tidy-up.
- If gas appliances are to be relied on, book a Gas Safe engineer and list both.
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 a warm cylinder prove the combi is off?
No. Warmth can come from either source, or from an immersion. The survey did not separate them.
Is an old cylinder automatically a defect because a combi exists?
No. It may still be in use. Abandoned, if it is abandoned, is a later finding, not a glance.