Toilet Cistern Filling Slowly

What's happening?

After a flush the inlet (fill) valve opens and refills the cistern until the float lifts and shuts it. Slow refilling means water arrives slowly, so the question is where the restriction sits. The isolating valve on the supply pipe may be part-closed, the valve's small inlet filter may be clogged with scale or grit, the flexible connector may be kinked, or the cistern may be on a supply that is weak everywhere. Some modern cisterns also slow the refill on purpose to cut noise, so check the maker's note first. A cistern that is slow to refill but never stops is a different fault: see the toilet keeps running page.

What usually causes it?

• Isolating valve under or beside the cistern left part-closed after earlier work
• Inlet valve filter or seat blocked with scale, grit or debris
• A kinked or crushed flexible tap connector
• A float arm set so the valve closes before the cistern is full, then hunts
• Low pressure on the supply to the toilet, often a gravity-fed branch
• A delayed-fill valve designed to refill slowly to quieten the flush
• A partly blocked pipe to the cistern after plumbing work elsewhere

Is it dangerous?

No. The cost is a toilet that cannot be flushed twice in a row, and a small hardship for a household in the morning. Left alone, a scaled inlet valve gets worse until it does not shut off cleanly and starts leaking into the pan.

Can I fix it myself?

Check the isolating valve first: it should be fully in line with the pipe, a slot parallel to the pipe or a lever along it. Then shut it off, flush to empty the cistern, take the lid off, and unscrew the top of the inlet valve to rinse out its filter or washer under a tap. Check the flexible connector for kinks. Turn the supply back on slowly and time the refill. If other taps in the house run poorly too, the cause is upstream: see the low water pressure page. Do not take the inlet valve to pieces beyond what the maker shows; parts are not interchangeable between brands.

When should you call a plumber?

Call a plumber when the isolating valve is stiff or leaks when moved, when cleaning the inlet valve does not help, when the cistern is on a low-pressure or tank-fed supply that needs a different valve, or when the toilet sits behind a panel.

What will the plumber actually do?

• Check flow at the isolating valve and at the connector to separate a supply fault from a valve fault
• Clean or replace the inlet valve and its filter, and match the valve to the supply type, high or low pressure
• Replace a stiff or leaking isolating valve so the toilet can be isolated in future
• Replace a kinked connector and reset the water level to the marked line
• Check the supply to the toilet if other outlets are also slow

Who fixes this

• Toilet repair and replacement
• Low water pressure fix

What it usually costs

Low Water Pressure Pump Cost

£400–£600

Questions people ask

Sources & References

1. WaterSafe: why is my toilet filling slowly
2. The Water Supply (Water Fittings) Regulations 1999, Schedule 2