Toilet Cistern Not Filling With Water

Start with the cold tap next to it

Turn on the cold tap at the basin in the same bathroom. It tells you straight away whether the problem is the toilet or the water reaching it.

• No water from the tap either: the supply is off. Check whether neighbours have water, and look for a notice of works from your water company. If they have water and you do not, see our no-water emergency call-out.
• A weak trickle from the tap: low supply pressure, a partly closed stopcock or a frozen pipe in cold weather. The cistern will fill, but very slowly.
• Normal flow from the tap: the supply is fine, and the fault is in the toilet's own isolation valve, feed pipe or fill valve.

In some older houses and flats, the toilet may be fed from a cold water tank in the loft rather than directly from the mains. If the basin cold tap is mains-fed and the toilet is tank-fed, check the tank has water in it and its own ball valve is working.

Is the isolation valve open?

Most toilets have a small isolation valve on the pipe just before the fill valve. It is a slotted screw, a small lever or a little handle. When the slot or lever runs along the line of the pipe, it is open. Across the pipe, it is shut.

These get closed during other work and left that way, or knocked half shut by cleaning. Open it fully with a flat screwdriver. If it is stiff, turn it gently back and forth; forcing a corroded valve can snap the spindle or start a leak around it. If the valve leaks or will not move, turn the water off at the main stopcock and have it replaced. Our page on stopcock repair covers a main stopcock that will not turn.

A blocked or failed fill valve

If the tap runs normally and the isolation valve is open, lift the cistern lid and flush. Watch the fill valve. If there is no sound at all, or just a faint hiss with no water coming out, the valve is blocked or stuck shut.

Grit is the usual cause, and it often arrives after water mains work in the street or after the water has been off. Many modern fill valves have a small mesh filter where the pipe connects, and most have a diaphragm washer under a top cap. With the isolation valve shut, unscrew the cap, lift out the washer and rinse it and the seat under a tap. Put a cup over the open valve and turn the isolation valve on briefly: the burst of water flushes grit from the inlet. Reassemble and test.

If the valve still will not open, it has failed. A new fill valve costs roughly £10 to £25. Buy one that fits the cistern's inlet position, side or bottom entry, and suits your supply pressure. Our guide to a leaking toilet inlet valve explains the different types.

A stuck float or a slow fill

The float rises with the water and closes the valve. If it has been pushed up and caught on the cistern wall, the lid, the flush valve or its own linkage, the valve stays closed with an empty cistern. Lower it gently by hand. If water starts flowing, free whatever was trapping it and check it moves through its full travel.

A cistern that fills but takes five, ten or fifteen minutes has a partial restriction, not a failure, and flushing before it is full gives the half-hearted result described in a toilet not flushing properly. Check the isolation valve is fully open, clean the filter and the diaphragm washer as above, and check the supply pressure at the tap. On a tank-fed supply, a fill valve made for mains pressure can fill painfully slowly because its opening is too small for the low pressure. The fix is a valve or seat rated for low pressure. Our page on low water pressure repair covers pressure problems across the house.

Frozen pipes and air locks

In a cold snap, a toilet on an outside wall, in an extension or fed through the loft is often the first fitting to stop filling. If the tap in the same room is also slow and the pipe to the toilet feels ice-cold, it is probably frozen. Turn off the main stopcock, leave the isolation valve and the basin tap open, then thaw the pipe gently with a hairdryer on low or warm cloths, starting at the valve end. Check for leaks before turning the water back on. Never use a naked flame. Our guide to frozen pipes covers what to watch for as it thaws.

An air lock can stop a tank-fed toilet filling after the system has been drained. It shows as spluttering or no flow even though the tank is full. Clearing one sometimes needs mains pressure pushed back through the pipe, which is a job for a plumber if the pipework is not arranged for it.

Flushing while you wait, and getting it fixed

You can still use the toilet. Pour a bucket of water, about 6 litres, into the bowl in one go and it will flush. Or fill the cistern from a bucket and press the button as normal. Our page on how to flush without water covers this.

If the fault is at the toilet, a toilet repair visit covers finding it, clearing or replacing the fill valve and setting the water level. It is a £60 call-out at any hour, and the repair price is agreed with you on site before any work starts. Across London, replacing a fill valve on an ordinary toilet typically costs in the region of £80 to £150 including the part. Concealed cisterns cost more because everything is reached through the flush plate.