A backup water tank only earns its keep if it actually fills, holds and delivers water when the municipal supply drops. When it won't fill — or won't stop overflowing — the fault is usually simple. Here's how to read it.
Tank won't fill
- Stuck or faulty inlet float valve — the most common cause; it isn't opening to let water in.
- Closed or partly-closed supply valve feeding the tank.
- Low municipal pressure not reaching the tank.
- Changeover set wrong, so the tank isn't being fed.
Tank keeps overflowing
An overflow means the inlet float valve isn't shutting off when the tank is full — it's stuck open or worn. Adjusting or replacing the float valve stops it; ignored, it wastes water continuously.
Tank full but house has no water
If the tank holds water but the house doesn't draw from it during a cut, the automatic changeover isn't switching over, or the pump isn't running. A faulty changeover valve, pump, or incorrect setup is to blame — a plumber checks both.
Keep it working
Float valve, changeover, pump and pressure should be checked periodically so the system works when you need it. We install and service backup water systems — book a service.