Electrics and gas
An unvented cylinder has a discharge pipe that disappears into the wall. What relief path has not been traced to the outside?
The relief path that has not been traced is the discharge from this unvented cylinder to the outside. The pipe leaves the cylinder and disappears into the wall. The survey has not seen where it emerges, whether it is the safety discharge, or whether it ends in a visible, safe position. A home survey is not a gas or plumbing commissioning test. An unvented cylinder relies on its relief route when something goes wrong. That route, beyond the wall, was not followed, so it remains an untraced path rather than a confirmed one.
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?
Unvented cylinders store hot water under pressure, which is why the discharge arrangement matters and why a pipe vanishing into construction is an incomplete observation. The surveyor can see the cylinder, the tun-dish if one was visible, and the point the pipe enters the wall. They cannot see behind the plaster. Guessing that it falls to a gully because houses often do that is how reports overclaim. This report, if it is careful, stops at disappeared.
Ask a competent plumber, or the engineer who deals with this cylinder, to trace the discharge to its end and to say what they found in writing. Ask the seller for any commissioning or service note for the cylinder. Do not knock holes in the wall yourself to chase the pipe. The survey's contribution is the limit: a discharge pipe goes into the wall and was not traced outside. Until someone traces it, the relief path is unfinished business, not a detail you can assume.
What should you ask your surveyor?
- Where did the discharge pipe disappear, and where did you look outside?
- Did you see a termination, or only the entry into the wall?
- Are you leaving the relief path as untraced rather than assumed?
What are the typical next steps?
- Record the discharge pipe as not traced to the outside.
- Do not assume it ends at a gully you have not tied to this pipe.
- Ask a competent person to trace the relief path and record the end.
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 a pipe drips outside somewhere, is it this discharge?
Not unless it was traced from this cylinder. Another drip can belong to a condensate or a waste. The survey has not followed this relief pipe to the outside, so a random drip does not identify it. Trace it before you name it.
Does a tun-dish under the cylinder finish the path?
No. A tun-dish, if visible, is a break in the pipework near the cylinder. It does not show where the pipe goes after it enters the wall. That outside end is still untraced. The wall still hides the rest of the route.