Fix a toilet that keeps running

Diagnose and fix a running toilet cistern by isolating the water, draining it, and replacing the worn valve or siphon washer.

AB-01Work out why the toilet keeps runningTake the lid off the cistern and watch where the water is going. If it trickles constantly into the overflow pipe outside the house, the inlet (float) valve is at fault. If it keeps trickling into the toilet pan even after flushing has stopped, the flush mechanism inside the cistern is leaking. Note which one it is before you start, so you buy the right part.

AB-02Turn off the water supplyFind the isolation valve on the pipe feeding the cistern, usually behind or beside the toilet, and turn it clockwise with a screwdriver or by hand until it stops. If there isn't one, turn off at the main stopcock, usually under the kitchen sink, and check beforehand that it actually turns. Flush the toilet to empty as much water from the cistern as possible.

AB-03Drain the cistern fullyLay an old towel on the floor and put a bucket under the cistern. Sponge out any water left in the bottom. Use an adjustable spanner to loosen the nut connecting the flexible supply pipe to the underside of the inlet valve, and let the last bit of water drip into the bucket.

1 each · Bucket

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1 each · Adjustable spanner

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1 each · Old towel or cloth

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AB-04Identify your flush mechanismOlder cisterns usually have a siphon: a plastic tube in the middle with a diaphragm that lifts when you pull the lever. Newer dual-flush cisterns usually have a valve instead, with a rubber seal like a large bath plug that lifts off its seat. With the cistern empty, operate the flush and watch which type moves, so you fix the right part.

AB-05Fix a leaking inlet valveIf water trickles into the overflow even when the cistern is full, the float valve's washer has worn out or the valve itself has failed. Unscrew the cap on the valve and replace the diaphragm washer inside, or fit a whole new float valve if it's badly worn. Wrap the threaded tail in PTFE tape before reconnecting the supply pipe.

RULES

1 each · Replacement float valve (WRAS-approved)

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1 roll · PTFE tape

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KNOW THE RULES

Any replacement float valve must be WRAS-approved, as required under the Water Supply (Water Fittings) Regulations 1999.

AB-06Fix a leaking siphonIf your cistern has a siphon and water keeps running into the pan, the diaphragm at the bottom of the siphon tube has likely perished. Undo the nut linking the siphon to the flush lever, lift the whole siphon assembly straight up and out, and replace the flap or washer at its base. Refit the siphon and reconnect the lever.

1 each · Siphon washer/diaphragm kit

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AB-07Fix a leaking valve-type flushIf your cistern has a drop valve instead of a siphon, the rubber seal at its base has probably hardened or warped and no longer seats properly. Unclip the valve body, lift it out, and fit a new seal or a whole replacement valve unit, making sure it sits flat and centred on its seat.

RULES

1 each · Replacement flush valve seal or unit (WRAS-approved)

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KNOW THE RULES

Replacement flush valves and seals should be WRAS-approved to meet UK Water Fittings Regulations.

AB-08Check and adjust the float heightThe water level should sit about 25mm below the overflow pipe outlet. On modern valves, turn the adjustment screw or slide the float along its arm. On older ballcock-type valves, gently bend the metal arm downward. This stops the cistern overfilling and running into the overflow again later.

AB-09Reconnect and refillReconnect the flexible supply pipe to the valve, hand-tighten the nut, then give it a quarter turn with the spanner. Turn the water back on slowly and check the joint for drips. Flush the toilet several times and watch the cistern refill and stop cleanly.

AB-10Tidy up and do a final checkWipe the cistern and floor dry, and recycle or bin the old washer or valve. Leave the toilet alone for ten minutes, then check the cistern hasn't started trickling again and there are no drips underneath.

1 each · Cloth or sponge

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