Radon
A radon sump fan is fitted and it was switched off on the day. What has the survey not measured about the radon in the house?
Not the radon. A sump fan that was switched off on the day means the survey has not measured the radon in the house. The fan is a piece of equipment. Off, on, or missing a test, it is not a concentration. A home survey looks at what is there. It does not run a radon measurement, and a silent fan does not stand in for one. You know a system was fitted and that it was not running during the visit. You do not know the radon level with the fan off, or what it would be if the fan were running.
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?
UKradon publishes an Action Level and a Target Level, and it publishes maps. Neither a leaflet threshold nor a map colour is a reading taken in these rooms while the fan was off. The surveyor can record the sump, the fan, and that the fan was switched off. That is a description of plant. It is not a result. Do not let a seller's comment that the fan is usually on become the measurement the visit did not take.
If you want a figure for the house, you need a proper radon test, done in the way the measurement guidance expects, not a conclusion drawn from a switched-off switch. Ask where the fan serves, whether you saw a sump or only a box, and whether the surveyor heard it run. Until a detector has sat in the house, the report should not be read as saying the radon is fine, or that it is not. The fan's position that day left the level unmeasured.
What should you ask your surveyor?
- Where is the sump, and which rooms do you think the fan serves?
- Did you see the fan switched off, or only hear that it was?
- What would still be unmeasured even if the fan had been running?
What are the typical next steps?
- Record that the fan was off and that no radon reading was taken.
- Do not treat the fan as a measurement of the house.
- Arrange a radon test if you need a level for these rooms.
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 fitted sump prove the radon is under control?
No. A fitted fan, especially one that was off, is not a measurement of the radon in the house. The switch position is not a concentration.
Will the home survey quote a radon concentration?
No. The survey did not measure it. A test, not the inspection, is what produces a level, and a silent fan does not stand in for that test.