Domakihub How to Fix a Dripping Overflow Pipe Yourself
Stop that persistent drip before it wastes water or signals a bigger plumbing problem.
Reviewed by Domakihub home & decor pros · 2026-06-23 · 5 min read
A dripping overflow pipe on the outside wall of your home, holiday rental, or hotel is easy to ignore — until the wall staining appears or the water bill climbs. In Greece's hard-water regions, mineral scale makes float valves fail sooner than you might expect, so this is a repair most property owners encounter at least once. The video above walks you through the diagnosis and valve work hands-on; the steps below give you the full picture so you know exactly what you are doing before you start.
What Does an Overflow Pipe Actually Do?
An overflow pipe is a safety outlet built into your cold-water storage tank, toilet cistern, or expansion vessel. When the water level inside rises too high — because the float valve is not shutting off properly — water exits through this pipe to the outside of the building rather than flooding the room. A steady drip or trickle from that pipe is therefore not a leak in the usual sense; it is the system working as designed, but signalling that something upstream needs attention.
On most Greek properties built before the 2000s you will find a cold-water tank in the roof space (δεξαμενή). Newer builds may use a pressurised system without an open tank, but toilet cisterns with overflow pipes are universal. In each case the root cause of dripping is almost always the same: a float valve that no longer closes fully.
Diagnosing the Source Before You Start
Trace the overflow pipe from the outside wall back to where it enters the building, then follow it to the tank or cistern it serves. On a cold-water roof tank, lift the lid and watch the float. If the water level is sitting at or above the overflow outlet, the float valve is not shutting off. The ball float itself may have developed a crack and be sitting low in the water, or the valve washer inside the body may have perished and no longer seals. Both are inexpensive to fix.
For a toilet cistern, remove the lid and flush. Watch whether the float rises cleanly and whether the filling stops before water reaches the overflow pipe level. If it does not stop, or if you can hear water trickling continuously into the bowl, the cistern fill valve needs adjustment or replacement. Do not skip this diagnosis step — it determines which repair path you take.
Steps to Fix a Dripping Overflow Pipe
- 1
Shut Off the Water Supply
Locate the isolation valve or stopcock that feeds the tank or cistern — on a roof tank this is usually on the supply pipe entering the loft, on a toilet cistern it is behind or beside the toilet pan. Turn it clockwise to close. Flush the toilet or open a cold tap at the lowest point to drain the water down. This makes the float valve accessible and dry to work on.
- 2
Check and Adjust the Float Arm
Once the water level drops, inspect the float arm — the rod that connects the ball float to the valve body. On older brass valves it is a rigid metal bar you can bend gently downward by hand to lower the shut-off water level. On modern plastic Portsmouth or Torbeck valves there is an adjustment screw or clip. Lower the float arm setting so the valve closes about 25 mm below the overflow outlet. Restore the water supply briefly to test: if the dripping stops you are done.
- 3
Inspect and Replace the Float if Cracked
If the ball float has water inside it (shake it — you will hear sloshing) it can no longer rise high enough to shut the valve. Unscrew the float from the arm counterclockwise and fit a new one of the same size. Plastic float balls are available at any hardware shop (χρωματοπωλείο or υδραυλικά) in Greece for a few euros. Reattach, restore the water, and recheck the level.
- 4
Replace the Valve Washer or the Whole Float Valve
If adjusting the float arm does not stop the dripping, the rubber washer inside the valve body has perished and no longer seals against the valve seat. On a Portsmouth-type valve, close the supply, use pliers to slide out the split pin at the end of the float arm, remove the piston, and prize out the old washer with a screwdriver. Press in a new matching washer (or a complete piston assembly) and reassemble. If the valve body is corroded or the seat is visibly pitted, replace the entire float valve — the job takes under 30 minutes with adjustable spanners and PTFE tape on the supply connection.
- 5
Test, Restore Supply, and Monitor
Turn the water supply back on slowly and watch the tank or cistern fill. The float should rise and the valve should close cleanly with the water level sitting 25–30 mm below the overflow pipe. Go outside and confirm the overflow pipe has stopped dripping. Leave the water on for 30 minutes and check again — sometimes a marginal washer drips only once pressure has been sitting on it for a while. If the drip persists after a washer change, the valve seat needs re-grinding or a full valve replacement is the cleaner fix.
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FAQ
- Why is my overflow pipe dripping even though I replaced the washer?
- The valve seat itself may be scored or corroded, preventing any washer from sealing fully. You can test this by running a fingernail around the seat — if you feel ridges or pitting, the seat needs re-grinding with a valve-seat reamer tool, or the whole valve body should be replaced. In Greece's hard-water areas, calcium deposits on the seat are a common culprit worth checking before buying a second washer.
- Can a dripping overflow pipe cause structural damage?
- Yes, over time. Water trickling down an outside wall saturates the render, damages the substrate, and in cold winters can cause cracking as moisture freezes. On roof terraces common in Greek holiday properties, persistent overflow drips can stain plaster and promote mould inside wall cavities. Fix a dripping overflow pipe promptly — the part cost is negligible compared with external render repairs.
- Is this a job I can do myself or should I call a plumber?
- Adjusting the float arm or replacing a float ball are genuinely DIY tasks requiring no specialist tools. Replacing the washer or the full float valve is slightly more involved but well within the ability of a careful homeowner with a basic spanner set and PTFE tape. If the tank is in a confined roof space, the supply pipework is corroded, or you find the whole valve body needs replacement and the existing pipe fittings are old-style imperial sizes (common in pre-1990 Greek buildings), calling a licensed plumber for that specific stage is a sensible call.