Electrics and gas
The heating system was drained because the house is empty. What boiler performance could not be observed?
What could not be observed is the boiler actually performing. The heating system was drained because the house is empty, so there was no filled circuit to fire, no heat to feel and no circulation to watch. The survey has recorded an empty system. It has not tested the gas, has not seen the boiler run, and has not produced a gas-safety record. A drained boiler is an inspection limit, not a pass.
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?
Performance means the burner lighting, the controls calling for heat, radiators or the cylinder warming, and any obvious fault while it runs. None of that can be seen when the system has been drained down for an empty house. Looking at the casing, the flue terminal and the pipes is visual only. Gas Safe inspection and a landlord or homeowner gas check are different visits. This home survey did not carry them out, and a cold empty house does not stand in for them.
Ask the seller to fill and run the system for a proper look, or instruct a Gas Safe engineer once it can be fired, if you need performance rather than a visual note. Tell the solicitor the survey did not watch the boiler work. Do not tell a lender the heating was tested. Until it is filled, the report should keep saying the system was drained and performance was not observed.
What should you ask your surveyor?
- Was the heating drained, so the boiler could not be watched running?
- Did you leave gas safety and performance untested?
- What of the installation could you see without it being fired?
What are the typical next steps?
- Treat the drained system as untested performance.
- Do not describe the boiler as having been seen to run.
- Ask for a Gas Safe check once the system can be fired.
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 flue looks clean, has the boiler been proved?
A clean flue terminal is an outside appearance. It is not the boiler firing on a filled system. The survey could not observe performance because the heating was drained. Gas safety was not carried out either. Appearance is not a firing test.
Does an empty house make a gas test unnecessary?
No. Emptiness is why the system was drained. It does not test the gas and it does not show the boiler working. The home survey still has not watched performance, and a vacant house is not a gas-safety record. Vacancy is an access fact only.