Toilet Not Flushing Properly

A toilet that needs two or three goes, or that empties slowly and leaves the pan dirty, is not usually worn out. The flush is a simple mechanical event: a set volume of water dumped fast enough to create a siphon in the pan. Anything that reduces the volume or slows the dump gives you a weak flush. Work through the checks below in order and you will find the cause in most cases without buying anything.

Start by watching a flush with the lid off

Take the cistern lid off, put it somewhere safe on a towel, and flush while watching. You are looking for three things: how full the cistern was before, how quickly the water leaves, and whether the mechanism lifts fully and drops back cleanly. That thirty second observation tells you more than any amount of guessing.

Cause one, the water level is too low

The level should sit roughly 15 to 20mm below the overflow slot on the flush valve. If it is well below that, the flush has less water and less head pressure. Fill valves have an adjuster, either a screw on the top or a clip on the float arm. Raise it a little, let the cistern refill and test again. This alone fixes a surprising number of weak flushes.

Cause two, a worn flush valve or diaphragm

In a siphon type cistern the rubber diaphragm perishes and lets air through, so the siphon never really gets going and you get a limp, slow flush. In a drop valve cistern the seal ring hardens and lets water past continuously, so the cistern never fills properly and often you can hear a faint trickle in the pan. Both are common consumables and both are replaceable, though the cistern has to be drained and, on a close coupled unit, sometimes lifted off the pan.

Cause three, the button or lever is out of adjustment

Dual flush plates work by pushing two separate rods to two different heights. If a rod has unscrewed, or the plate spacers were set wrong when the wall was tiled, one or both flushes stop engaging fully. On a lever flush, a stretched or corroded link means the lift is short. These are adjustments rather than repairs, and they are usually reachable by hand.

Cause four, blocked rim holes

In hard water areas the small holes under the pan rim scale up over years. The flush volume is fine but the water cannot get around the bowl, so it dumps down one side and leaves the rest dirty. Hold a small mirror under the rim to look. Careful descaling with a proprietary limescale remover and a piece of wire will often restore the spread.

Cause five, a partial blockage or poor fall

If the pan fills up then drains away slowly, you have a restriction downstream rather than a flush fault. Common in cloakrooms and en suites where the waste run is long, has too many bends or was laid with too little fall. Rodding will clear a one off blockage, but if it happens repeatedly the pipe run itself needs looking at.

Cause six, the pan is simply old or the wrong match

Rimless and modern low volume pans are designed around a specific flush volume. Fitting a new cistern to a very old pan, or vice versa, can leave you with a combination that never performs. If a toilet has never flushed well since the day it was fitted, that is usually why.

Safe things to try yourself

• Adjust the fill level up slightly and retest.
• Check the flush rods and linkage for a loose or dropped connection.
• Descale the rim holes if you are in a hard water area.
• Pour a bucket of water quickly into the pan. If it clears well, the pan and waste are fine and the fault is in the cistern.

What we would leave alone is anything that involves breaking a tiled wall to reach a concealed cistern, or lifting a close coupled cistern off a pan without new bolt seals ready.

Fitting help across Stoke-on-Trent

We repair and replace toilets, concealed frames and cisterns, and we fit them as part of full bathrooms and cloakrooms. Send us a message with the make and what it is doing, or read about our cloakroom and WC work. Free survey, fixed written price within 24 hours.

Common questions