Fix a dripping overflow pipe outside

Trace the drip to a worn float valve, isolate the water, fix or replace it, then test the overflow.

OP-01Find out where the drip is really coming fromAn overflow pipe dripping outside almost always means water is getting into a toilet cistern or a cold water tank (usually in the loft) faster than it can shut off. Follow the white or grey overflow pipe back indoors to see which fitting it connects to. If you have a loft tank, check that one first, since a slow drip outside can mean it's been running for a while unnoticed.

1 each · Torch

Buy:ScrewfixB&QToolstationAmazon

OP-02Turn off the water supply to that cistern or tankFor a toilet, close the small isolation valve on the pipe under or behind the cistern, usually a slotted screw you turn a quarter turn with a screwdriver. For a loft tank with no isolation valve, turn off the main stopcock, usually under the kitchen sink, and check it actually turns before you rely on it. Flush the toilet or run a tap to empty water out of the system so it stops refilling while you work.

1 each · Flathead screwdriver

Buy:ScrewfixB&QToolstationAmazon

OP-03Drain enough water to work safelyFlush the toilet with the isolation valve shut, or if it's a loft tank, tie the float up and let the tank run down through normal use before opening it. Have an old towel and a bucket ready, some water will still be sitting in the cistern or tank. Wear old clothes, loft tanks especially can be grim inside.

1 each · Bucket

Buy:ScrewfixB&QToolstationAmazon

1 each · Old towel

Buy:ScrewfixB&QToolstationAmazon

OP-04Lift the lid and inspect the float valveLift off the cistern lid or open the tank lid and look at the float valve, the plastic or brass fitting with an arm and a ball or float attached. An older brass 'Portsmouth' valve has a piston that can wear or jam; a modern plastic valve, often branded Torbeck or similar, has a diaphragm that perishes over time. Check if the float arm is bent, the float has filled with water and sunk, or the valve simply won't shut off even when the float is fully up.

OP-05Adjust the float level first, it's the free fixIf the valve shuts off fine but the water level is set too high, it will trickle into the overflow every time it fills. On a brass arm, gently bend it downward to lower the shut-off point. On a plastic valve, there's usually an adjustment screw or a notched arm, turn or reposition it to lower the water level by 10-15mm. Turn the water back on briefly to test before doing anything more.

OP-06Replace the washer or the whole valve if adjustment doesn't fix itFor an old brass valve, unscrew the cap on the end, pull out the piston and fit a new washer, sold in packs to fit 15mm valves. For a worn plastic valve, it's usually easier and cheaper to fit a whole new equilibrium-type valve rather than repair it. Undo the tap connector nut with an adjustable spanner, wrap the new valve's threads with 2-3 turns of PTFE tape, and screw it in hand-tight plus a quarter turn.

RULES

1 each · Equilibrium float valve (15mm)

Buy:ScrewfixB&QToolstationAmazon

1 pack · Ball valve washer pack

Buy:ScrewfixB&QToolstationAmazon

1 roll · PTFE tape

Buy:ScrewfixB&QToolstationAmazon

1 each · Adjustable spanner

Buy:ScrewfixB&QToolstationAmazon

KNOW THE RULES

Any replacement float valve fitted must be an approved type under the Water Supply (Water Fittings) Regulations 1999. Buy one sold as WRAS-approved and you'll be covered; cheap unbranded valves sometimes aren't.

OP-07Check the overflow pipe itself while you're thereLook at the pipe run from the cistern or tank out through the wall. It should fall gently downward all the way to outside, with no dips where water can sit and freeze in winter. If the pipe sags or has a low point, this can also cause dripping long after the valve is fixed, and may need a cable tie or clip to lift it straight.

2 each · Pipe clips

Buy:ScrewfixB&QToolstationAmazon

OP-08Turn the water back on and test properlyOpen the isolation valve or stopcock fully and let the cistern or tank fill. Watch it fill completely and shut off on its own, then flush or draw water and let it refill a second time to be sure. Check outside that the overflow pipe has stopped dripping once the water has settled for a few minutes.

OP-09Tidy up and dispose of old partsDry off the cistern or tank area and put the lid back on. Wipe down any spilled water around the loft tank, standing water there can stain ceilings below. Bag up the old valve and washer, most can go in general waste.

Some links may earn us a small commission at no extra cost to you.

Save this as a project

Back to all guides