First: what pipe is actually dripping?
People quite naturally call any little pipe outside an “overflow pipe”, but sometimes it is not an overflow at all. It could be a pressure-relief discharge from a sealed heating system or a temperature/pressure-relief discharge from an unvented hot-water cylinder.
High up / roof / soffitOften an overflow from a cold-water storage cistern or a central-heating feed and expansion cistern in the loft.
Halfway up the wallOften an older-style toilet cistern overflow, depending on what is on the other side of the wall.
Copper pipe lower downMay be a safety discharge from a sealed heating or pressurised hot-water system. That needs proper investigation.
Not sure? Send me a photo on WhatsApp showing the pipe and where it comes out of the building. In many cases I can tell you straight away what type of pipe you are looking at.
Overflow from a tank in the loft
Older UK homes can still have gravity-fed systems with a cold-water storage cistern and/or a small feed and expansion cistern in the loft. They are old technology now and I very rarely install systems like that, but there are still plenty of them in existing houses.
If water is coming from an overflow high up near the roof, the most common thing I find in day-to-day work is an old fill valve — what most people call a ball valve — that is no longer shutting the incoming water off properly.
Sometimes the float cannot rise properly because something is obstructing it. I have even found makeshift covers or insulation that have become wet and held a float down.
Another possibility is “pumping over”. On an older open-vented heating system, circulation problems or restrictions can cause heating water to discharge back into the feed and expansion cistern. That is a different fault from a simple failed ball valve and the heating system needs investigating.
If it is a toilet overflow
If an older toilet has a separate overflow pipe through the wall and water is coming out of it, the overflow itself is normally doing exactly what it was designed to do. The problem is usually that the cistern fill valve is not shutting off when the water reaches the correct level.
Without the overflow, that excess water would have to go somewhere else — potentially into the house. The repair is normally straightforward: identify the faulty fill valve, replace it, set the water level correctly and test the cistern.
Can I just leave a dripping overflow?
You can, but it is not particularly sensible. You are wasting water and, if you are on a water meter, you are paying for it. A small continuous trickle can add up.
There is another reason I would not ignore it. I have attended jobs where the customer thought they had a burst pipe because water was coming through the ceiling. The actual problem was an overflowing loft cistern combined with an overflow pipe that was damaged or leaking inside the property. A pipe that has never had to carry much water before can reveal a weakness as soon as it is suddenly asked to do its job.
In other words: the overflow is a warning. Fix the reason the water level is getting too high rather than waiting for the warning to turn into water damage.
What if the outside pipe is copper?
Do not automatically treat a copper discharge pipe as a simple tank overflow. A pipe turned back towards the wall may be connected to a pressure-relief or temperature/pressure-relief safety valve. It is arranged that way so a discharge — which may be hot — is directed safely towards the wall rather than at somebody walking past.
If one of those pipes is discharging, something is not right with the sealed heating system or pressurised hot-water system. That is a job for a suitably qualified heating engineer to identify why the safety device is operating.
How I repair a failed loft ball valve
This is bread-and-butter plumbing for me. Once I have confirmed the fill valve is the fault, I normally replace the complete valve and fit a new float rather than trying to resurrect an old, scaled-up valve that may have been sitting in the loft for years.
I carry the common Part 1 and Part 2 ball valves and new floats, so if the customer has described the problem properly — or sent me a photo — I can normally arrive prepared for what I am likely to find.
Valve life varies enormously with age, water conditions and installation. My preference is simply to make a reliable repair rather than spend the customer's money patching an old valve that may fail somewhere else soon afterwards.
Water coming out of a pipe outside your house?
If you do not know whether it is a loft overflow, toilet overflow, boiler discharge or hot-water-cylinder discharge, do not worry about naming it. Send me a clear photo showing the pipe and roughly where it comes through the outside wall.
I would rather identify what you are actually looking at first, then work out the sensible repair.
S R Francis Ltd provides plumbing repairs across Bromley, Bickley, Beckenham, Hayes, Keston, Petts Wood, Orpington, Chislehurst, Biggin Hill and the immediate surrounding area.
