Quick answer
A cistern that will not fill has a closed stop-cock at the wall, a blocked inlet filter, or a stuck or failed inlet valve. Start at the wall: the isolation valve is frequently closed accidentally during other work and forgotten. If the valve is open and water still will not enter, the small filter screen in the inlet valve is usually clogged with grit from the supply.
Common causes
- Wall isolation valve closed, often after unrelated plumbing work
- Clogged inlet filter screen full of grit or scale
- Float stuck in the raised position so the valve stays shut
- Failed inlet valve diaphragm
- Low supply pressure, particularly in a cistern fed from a gravity tank
- Kinked or crushed flexible connector behind the cistern
What you can do now
- 1Check the wall stop-cock is fully open — turn it fully and back a quarter turn
- 2Close the stop-cock, remove and clean the inlet filter screen, and refit
- 3Check the float moves freely and is not caught on the cistern wall or the overflow
- 4Look at the flexible connector for kinks or crushing behind the cistern
- 5Test another tap nearby to confirm you have supply pressure at all
When to call a professional
If the valve is open, the filter is clean and the float moves freely, the inlet valve has failed and needs replacing — a quick job with the right part. Call sooner for a concealed or wall-hung cistern, where access runs through the flush plate and forcing it risks damaging the wall finish.
Typical cost in Johannesburg
Inlet valve R350–R650
Indicative ranges only. We provide written, itemised quotes before any work.
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