Drainage and septic tanks
A treatment plant has an alarm box and the power was off on the day. What treatment performance was not observed?
Treatment performance was not observed. The plant has an alarm box, and the power was off, so the process the plant is meant to run was not seen working. No sample was taken, no motor or blower was heard, and the alarm was not tested. The survey records the box and a plant with the supply off. It has not decided that the plant treats properly, and it has not decided that it has failed. The day simply did not show performance.
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?
A treatment plant needs power for the aeration or pumping that separates it from a plain tank. The alarm is there to say when that process stops. With the supply off, the surveyor sees a silent box. Silence is not a pass, and it is not a recorded failure of the treatment standard. No effluent was sampled. The unobserved thing is performance: whether the plant, when powered, treats as it should and whether the alarm would sound if it did not.
Have the power restored and ask the plant's maintainer to run it and report on the alarm before you rely on it. Service papers, if the seller has them, belong with the solicitor, and they are not a substitute for a plant that was off on the day of inspection. The survey cannot be reread into a test. Tell anyone who asks that treatment performance was not observed because the supply was dead.
What should you ask your surveyor?
- Was the power off, so the plant and alarm were not seen working?
- Was any sample of the discharge taken?
- Have you avoided both a pass and a fail on performance?
What are the typical next steps?
- Record that treatment performance was not observed.
- Do not call a silent, unpowered plant a pass or a fail.
- Have the maintainer run the plant and the alarm once power is on.
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 alarm box looks new, was performance still unseen?
Yes. A new box is a piece of equipment. It does not show the plant treating, and it does not show the alarm has been tested. The power was off. Performance remains unobserved whatever the age of the plastic housing.
Should the supply be on before a specialist comments on treatment?
If they are to watch the process, yes. A specialist can still identify the model with the power off. They cannot observe treatment performance until it can run. The home survey did not have that chance, and it has not pretended otherwise.