Toilet Flushing Problems: Why a Toilet Flushes Weakly, Runs On or Refills Slowly, and What to Do

Flushing problems are among the commonest complaints in any flat, and every RUAP flat has four toilets. A cistern has only a handful of moving parts, and most faults show clear symptoms once you lift the lid and watch one flush. If water is escaping from the toilet or cistern, see how to find and fix bathroom water leaks.

How a toilet flush works

A cistern stores a measured amount of water and releases it quickly. The fill valve (also called the inlet or float valve) lets water in and shuts off when a float rises with the water. The flush valve in the bottom of the cistern holds the water in until you press the button or lever, opens to let it rush into the pan, then closes so the cistern can refill.^[5] Many push-button cisterns, including concealed ones, use an upright drop valve worked by actuator rods; older and lever-operated toilets often use a rubber flapper on a chain.^[9]

Water enters the pan through small holes under the rim and, on many designs, a jet near the bottom that drives water into the trapway, the curved channel that carries waste away and holds a water seal against smells.^[1] An overflow tube sends excess water into the pan, so a fill valve that will not shut off shows up as a steady trickle into the bowl, not a flood.^[5]

Symptoms and their usual causes

Weak or incomplete flush

If the bowl does not clear, start inside the cistern. Fluidmaster, a maker of cistern valves, says a water level more than about an inch (2.5 cm) below the top of the overflow may not give a strong flush, and suggests raising it with the fill valve's adjustment screw.^[1] Too high is also a fault: Kohler says that if water reaches the overflow, the toilet will keep running.^[6]

Next, a flush valve that closes too soon: on a flapper toilet, a slack chain lets the flapper drop before the cistern empties, and Fluidmaster suggests only about half an inch (around 1 cm) of slack.^[1] Then scale: minerals can build up in the rim holes and jet until they restrict the flow.^[1]

If none of these is the cause, look downstream. Kohler links a slow flush, water rising in the bowl, gurgling drains and having to hold the handle down to poor venting or a blocked waste stack, a drainage problem covered below.^[7]

Double flushing

Needing a second flush is usually the weak-flush problem in another form: too little water is released because the level is low or the valve shuts early. On dual-flush valves with adjustable volumes, the setting may simply be too low. Fluidmaster's method is to start at the maximum, then step down one setting at a time, testing with a few sheets of toilet paper, until the bowl no longer clears, and go back up one.^[4] It also notes that if the water level is too low, the valve can close as soon as you let go of the lever.^[4]

Slow refill

A cistern that takes many minutes to refill is starved of water. Fluidmaster names debris in the fill valve, supply hose or wall shut-off valve as the usual cause, and says fill valves start to wear after about seven years.^[2] Reduced supply pressure is the other main cause.^[5] In a tall building that often depends on your floor (see the low-pressure section below).

Running toilet, or one that refills by itself

A hiss or trickle long after the flush means water is going in and straight out again. If the level rises until it spills into the overflow, the fill valve is not shutting off, often because grit is caught under its seal.^[6] If the level is right but the cistern refills briefly every so often, water is seeping past the flush valve seal; Fluidmaster warns this is often mistaken for a fill valve fault.^[5] Rule out two simple causes first: a refill tube pushed too far down inside the overflow,^[3] and a lever arm or chain that catches and holds the valve slightly open.^[6] The dye and tissue tests for a cistern-to-pan leak are in our bathroom leaks guide.

Button or lever faults

If the button or lever moves but nothing happens, the link to the flush valve has failed: a chain off its hook, a broken lever arm, or rods or a cable out of adjustment. If the toilet runs until you press again, the link may be holding the valve open, for example a sticking lever or a button that does not spring back.^[6] On a concealed cistern the rods sit behind the flush plate (see below).^[9]

Blockage or flush fault? Tell them apart first

Before adjusting the cistern, watch the bowl. With a cistern fault the flush is feeble, but the bowl water settles back to its normal level. With a blockage or venting problem the bowl water rises higher than normal and falls slowly, sometimes with bubbles or gurgling from other drains.^[7] If the cistern empties properly and the bowl still rises, the cistern is not the problem.

Many blockages start with things that should never be flushed. The UK water company Thames Water asks people to flush only pee, poo and toilet paper, and says even wipes sold as 'flushable' can block sewers.^[12] Keep a lidded bin in every bathroom.

Tools and materials you will need

• A torch and a towel to protect the floor; the cistern lid is heavy ceramic, so decide where you will rest it safely.
• A flat-head screwdriver to close and reopen the isolation valve, and an adjustable spanner.
• A plastic cup for flushing grit out of the fill valve.^[2]
• A short length of stiff wire or an old wire hanger, a small mirror and a limescale bowl cleaner for the rim holes.^[1]
• The toilet's make and model, or photos of the parts, before buying spares; concealed cisterns have a model code printed inside.^[9]

Step by step: diagnose and fix a flush fault

Work through these steps in order and test after each change.

1. Rule out a blockage first, as in the previous section. If the bowl rises and drains slowly, stop and treat it as a drain problem.
2. Lift the lid, rest it somewhere safe and watch one flush and refill: does the cistern empty fully, how long does it take to refill, and where does the water settle?
3. Check that the isolation valve on the supply pipe is fully open.
4. Compare the water level with the mark inside the cistern or the overflow. If it is more than about 2.5 cm below the overflow top, raise it with the fill valve's screw or clip; if water spills into the overflow, lower it.^[1][6]
5. On a flapper toilet, leave about 1 cm of chain slack, and make sure the chain cannot catch under the flapper or round the lever.^[1][6]
6. On a dual-flush valve, check that both buttons lift the valve fully and no volume dial or slide has been turned down.^[4]
7. If refilling is slow or the valve will not shut off, clean the fill valve: water off, flush, remove the valve cap as the maker shows, check the seal for grit, then hold a cup upside down over the valve and run the water fully for 10 to 15 seconds.^[2]
8. Clip the refill tube to the top of the overflow so it pours in from above; do not push it down inside.^[3]
9. If the flush is still weak, drain the cistern, pour a limescale bowl cleaner down the flush valve opening, leave it for several hours or overnight, then work a wire through the rim holes.^[1]
10. Turn the water on, flush several times, and refit the lid only when the bowl clears and the cistern goes quiet after refilling.

Concealed cisterns and flush plates

Many newer bathrooms hide the cistern in a frame behind the tiles, with only the flush plate showing. Inside are the same parts as in an exposed cistern: an isolating valve, a fill valve and float, a flush valve, and actuator rods from the buttons, reached through the opening behind the flush plate and its protection plate.^[9]

Geberit, a major maker of concealed cisterns, says a flush that keeps running is often caused by debris trapped between the flush valve seal and the outlet; the valve can be taken out, rinsed or wiped clean, and refitted.^[8] It advises against descaling the inside of the cistern, because loosened scale can break away and block it.^[8] Order parts using the model code printed inside the cistern, not a sticker on the protection plate, which Geberit says is not linked to the product code.^[9]

If the plate will not come off easily, or you cannot see how the valve unlocks, stop and call a plumber. A concealed cistern can leak into the wall unseen, so check the wall and the area below the pan for damp over the following days. For routine care of flush plates and other fittings, see our washroom fittings maintenance guide.

Low pressure, tall buildings and slow refills

In many Dhaka apartment buildings, water is pumped to a rooftop tank and flows down to the flats by gravity. The pressure at a cistern depends on the height of water above it, so top-floor flats just below the tank get the least; roughly, every 10 metres of height adds about one bar.

A fill valve still works at low pressure, only more slowly. The data sheet for one widely sold fill valve gives an operating range of 0.1 to 10 bar, with a flow of about 3.7 litres a minute at the bottom of that range and about 14 at the top.^[10] It also says the valve's flow restrictor must be removed on gravity-fed systems, which shows how a valve set up for mains pressure can refill very slowly from a tank.^[10] Check your own valve's instructions before removing anything, or ask a plumber.

If every tap and toilet on your floor is slow, the cause is probably the supply; see common causes of low water pressure in apartment buildings. When the rooftop tank runs dry during a supply cut or load-shedding, the cistern will not refill until the pump runs again; that is not a toilet fault.

Prevention: routine checks that keep the flush working

Avoid drop-in cistern tablets containing bleach or chlorine: Fluidmaster warns they can damage cistern parts and lead to flooding.^[1] A small notice in guest bathrooms asking people to bin wipes helps prevent blockages.^[12]

Common mistakes to avoid

• Bending the float arm or turning the level up until water spills into the overflow, so the toilet runs all the time.^[6]
• Taking every bit of slack out of a flapper chain; Fluidmaster and Kohler both suggest leaving a little.^[1][6]
• Replacing the fill valve because the cistern refills now and then, when the real fault is a leaking flush valve seal.^[5]
• Descaling the inside of a concealed cistern with acid; Geberit warns that loosened scale can block it.^[8]
• Buying 'universal' parts without checking the cistern model, especially for concealed cisterns.^[9]

Repair, replace or call a plumber?

Which faults most people can handle, and which need a plumber:

Replacing a whole fill valve or flush valve is a normal repair. Fluidmaster advises a new flush valve if a new seal does not stop the cistern draining down,^[5] and a new fill valve if cleaning does not cure it.^[2] Replace the toilet itself only if the pan is cracked, parts are no longer made, or it is old and very thirsty: the US Environmental Protection Agency (EPA) notes that older toilets can use up to 6 US gallons (about 23 litres) a flush, against 1.28 gallons (about 4.8 litres) or less for WaterSense-labelled models.^[11]

What drives the cost of a flush repair

We found no reliable published prices for toilet repairs in Bangladesh, so we give none. The cost depends mainly on:

• The part: a seal or flapper costs far less than a complete valve, and a valve far less than a new toilet; the EPA describes flappers as inexpensive and quick to replace.^[11]
• Matching: genuine parts for a particular concealed cistern may need ordering, while generic valves for exposed cisterns are easier to find.
• Access: an exposed cistern is a short job; a concealed one is worked through a small opening, and a frame fault may mean removing tiles.
• The call-out charge and any warranty on parts and labour.
• Waste while the fault continues: where water is pumped to a rooftop tank, a running toilet also costs pumping energy.

Ask for written quotes that name the part and its make, and compare them as explained in how to get and compare repair quotes.

Next steps

1. Today: if the bowl is filling up, stop flushing and close the isolation valve.
2. Lift the lid, watch one flush and use the chart above to decide which symptom you have.
3. Try the simple adjustments: water level, chain or rods, refill tube, then clean the fill valve.
4. If the flush is still weak, clean the rim holes; if the bowl drains slowly, follow the blocked-drain guide instead.
5. Call a plumber for a concealed cistern you cannot open, cracked ceramics or a fault that keeps coming back.
6. Add the monthly checks to your calendar for every toilet in the flat.