Radon
A radon fan in the cupboard was switched off. What protection is that fan not providing while it is off, and what level was not measured?
While it is switched off, that radon fan is not providing the underfloor extraction it is there to provide. A fan in a cupboard only moves air when it is running. Off, the sump or the subfloor path it serves is not being drawn, so the protection associated with the fan is not in operation. The survey has not measured a radon level in the house, switched on or switched off. It has recorded a fan that was off. It has not decided what the air in the rooms contains, and it has not tested whether the fan would work if someone turned it on.
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?
Radon systems of this kind rely on a fan to pull air from beneath the floor so soil gas is less likely to be drawn into the rooms. If the fan is off, that mechanism is idle. The surveyor can see a unit, a switch and perhaps a pipe. They cannot see a concentration, and a silent fan is not a reading. Presence without running is an installation that was not doing its job on the day.
Ask the seller, through the solicitor, why the fan was off, whether it is normally left running, and whether any service note exists. A reply is a statement, not a measurement. If you need to know the level in the house, that is a proper monitor over time, not a guess from a cupboard. Do not switch the fan on and off yourself as if that were a test the survey should have completed. The report's limit is the fan seen stopped, and no level taken.
What should you ask your surveyor?
- Did you see the fan stopped, and could you see where it discharges?
- Have you recorded that no radon level was measured on this visit?
- What would you need, beyond the fan being present, before commenting on protection in use?
What are the typical next steps?
- Treat the stopped fan as protection not running on the day.
- Ask why it was off and whether any service note exists.
- Do not read the cupboard fan as a radon measurement.
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 fan hums when switched on, has the level then been measured?
No. A hum shows only that the unit responded to a switch. It does not measure radon in the rooms, and the survey still has no result for the house either with the fan running or with it left off.
Does a sticker with a date replace the missing measurement?
No. A sticker is a mark that someone attended, if you can read the date. It is not a three-month reading, and it does not say what the fan was doing when the surveyor found it switched off in the cupboard.