Electrics and gas
The unvented cylinder's discharge pipe ends in an open hopper. Why is that a note for an engineer and not a certificate that the cylinder is safe?
Because the discharge pipe from the unvented cylinder ends in an open hopper, and that sighting is a note for an engineer, not a certificate that the cylinder is safe. The survey can record where the pipe went. It does not test the valves, the tundish, the temperature or the pressure, and it does not sign the cylinder off. An open hopper is simply where the pipe was seen to finish. Ask an engineer who works on unvented cylinders to comment on that termination before you treat the installation as cleared.
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?
An unvented cylinder stores hot water under pressure. The discharge pipe is the route that should carry water away if a control lifts. Seeing the end of that pipe in an open hopper tells you the termination that was visible. It does not tell you the valves work, that the pipe falls correctly along its whole length, or that the hopper is a suitable place for it to end. A visual note is not a safety certificate, and the survey does not issue one.
Give the engineer the survey sentence and, if you can, a photograph of the hopper, and ask them to inspect the cylinder, the tundish and the discharge route. Do not cap the hopper or reroute the pipe before completion. Do not read a dry hopper on the day as proof the controls are sound. Keep the engineer's comment with the report so the termination stays a question that was referred, not a pass the survey never gave.
What should you ask your surveyor?
- Did you see a tundish on the discharge pipe, or only the open hopper at the end?
- Was the pipe supported and visible along its run, or lost inside ducts?
- Any sign of water staining at the hopper, or was it dry on the day?
What are the typical next steps?
- Ask an unvented-cylinder engineer to inspect the discharge route.
- Do not cap the hopper or alter the pipe before completion.
- Keep their comment with the survey note rather than calling it a pass.
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 hopper was dry, is the cylinder safe?
No. A dry end on one day is not a test of the valves or the discharge route. The survey did not certify the cylinder.
Can you box the hopper in to tidy the wall?
No. Do not box the hopper in or move the pipe yet. Ask the unvented-cylinder engineer about that termination before anyone covers it.