Electrics and gas

Radiators are cold at the bottom and warm at the top. Is that a leak, and was a power flush done?

It is often sludge sitting in the radiator, which is a different note from a leak at a valve or a pipe. The survey did not power-flush the system, did not dose it, and did not pressure-test it. Warm metal is not a service record. Gas work, if the heat source is gas, is for a Gas Safe registered engineer.

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?

Cold bottoms with hot tops are a classic heating complaint. A damp patch under a valve is a different complaint. The survey should keep them apart. On a short visit the heating may be off, so every radiator is cold and the pattern cannot be seen. If the system was on, the surveyor can feel a sample of radiators. They cannot say how much sludge is in the pipes, and they must not describe a flush they did not do. Bleeding one radiator on a viewing is not a clean of the system.

A heating engineer, and a Gas Safe engineer where the boiler itself needs work, can advise whether a flush, a filter, or a repair is appropriate. The home survey does not choose the chemical. HSE’s gas guidance is about gas work, not about a certificate that the radiators are clean. An owner-occupier seller need not have a landlord gas record ready for you. Ask what servicing was done, and do not treat a warm top half as that service. There is no national price in the survey for a flush. Get a quote after someone has seen the system, and do not invent one.

What should you ask your surveyor?

Were the radiators on, and which ones were cold at the bottom?
Did you see leaks, as distinct from the cold metal?
Are you clear that no power flush was carried out?

What are the typical next steps?

Do not book a flush from a sentence that only says the heating was off.
If the pattern was felt, ask a heating engineer what they would do. Keep boiler gas work with a Gas Safe engineer.
Do not describe a stain on the ceiling as sludge in a radiator.

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

Is a cold radiator always sludge?

No. It may be off, air-locked, valved down, or failed. The survey did not take it apart.

Does a magnetic filter mean the sludge has already been dealt with?

No. A filter on the pipe is not a flush and not a service record.