Electrics and gas
What is a combi condensate pipe, and why is a drip under it not a roof leak?
A condensing boiler produces water that should run away through a small pipe, often to a drain. If that pipe leaks, blocks or has been poured into a gutter wrongly, you get a drip or a frozen stub in cold weather. That is a boiler waste, not a failed roof covering. The survey can see the pipe. It does not service the boiler.
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?
The pipe is plastic and narrow. Poor supports, a run that falls the wrong way, or a discharge into a place that freezes are common notes. Inside, a ceiling stain near the boiler may be this pipe rather than a tile. A Gas Safe engineer or a heating engineer deals with the boiler side. A roofer deals with the covering if the stain is nowhere near the pipe.
HSE’s gas guidance is about who may work on gas. Altering the boiler is that work. Altering only the plastic drain might be plumbing, but if it means moving the boiler’s condensate connection, stop and ask a registered engineer rather than guessing. Do not price a new roof for a condensate drip. Costs for re-routing a pipe are a small job until someone has seen it. This page will not invent the figure.
What should you ask your surveyor?
- Where does the condensate discharge, and did you see it?
- Is the stain near the boiler or under the covering?
- Are you recommending a heating engineer or a roofer?
What are the typical next steps?
- Trace the pipe before you instruct a roofer.
- Do not block the pipe to stop a drip. The boiler needs to discharge.
- If it discharges where people walk and it freezes, say that when you ask for a quote.
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
Is a condensate pipe a flue?
No. The flue carries combustion products. The condensate pipe carries water. Both matter. They are not interchangeable.
Does a new boiler include a new pipe run?
Only if the quote says so. Read it. A boiler swap that reuses a bad pipe repeats the drip.