You notice a pipe sticking out of the outside wall, dripping onto the patio. Or there's a steady drip by the front door that wasn't there last week. An overflow pipe is there to warn you that something inside is overfilling. The good news is that it's usually a simple fix.
Which pipe is it?
Follow the pipe back inside. It will usually lead to one of these:
- A toilet cistern. The most common cause. The fill valve isn't shutting off, so extra water runs out of the overflow.
- A cold water tank in the loft. Older homes often have one. A worn float valve keeps letting water in.
- The boiler. A copper pipe from the bottom of a combi boiler is usually the pressure relief pipe, not a normal overflow.
Toilet overflow dripping
Lift the cistern lid. If the water is above the overflow pipe, the fill valve needs adjusting or replacing. Lower the float so the water stops 2 to 3 cm below the overflow. Our guide on a toilet that keeps running walks you through it.
Loft tank overflow dripping
The float valve in the cold water tank lets water in until the float rises and shuts it off. When the washer wears or the float is set too high, the tank keeps filling. Adjusting the float or replacing the washer usually fixes it. Take care in the loft: stand only on joists or boards.
Boiler pipe dripping
If the pipe from your boiler is dripping, check the pressure gauge. If it's above about 2.5 bar, the boiler is releasing pressure to stay safe. This often happens after the system has been topped up too much. Don't take the boiler apart yourself. Any work inside a gas boiler must be done by a Gas Safe registered engineer. Our guide to boiler pressure explains the normal range.
Why not to ignore it
A dripping overflow wastes water, can stain brickwork and make patios slippery, and in freezing weather the drip can turn to ice. If the overflow suddenly runs fast instead of dripping, turn off the water to that toilet or tank and call a plumber.
Common questions
Why is my overflow pipe dripping?
Something inside is overfilling. Most often it's a toilet cistern whose fill valve doesn't shut off, or a loft tank with a worn float valve.
Is a dripping overflow pipe an emergency?
Not usually, but fix it soon. If it suddenly runs fast, turn off the water to that toilet or tank and call a plumber.
Why is my boiler overflow pipe dripping?
The pressure is usually too high, often above 2.5 bar, so the relief valve is letting water out. A Gas Safe engineer should check the boiler.