Water Tank Overfilling? Ballcock or Non-Return Valve Faults Explained
In most homes there are two water tanks – one located downstairs and one located upstairs (roof tank). Knowing which tank is overflowing helps identify the fault quickly and prevents unnecessary damage or pump wear.
Downstairs Tank – Ballcock Faults Only
The downstairs tank is fed directly from the mains water supply and is controlled by a single ballcock (float valve).
If this tank is continuously filling or overflowing, the cause is simple:
- Faulty ballcock allowing mains water to keep entering the tank
There is no non-return valve involved on the downstairs tank, so if it is flooding, the ballcock will need adjustment or replacement.
Upstairs (Roof) Cold Water Tank – Two Possible Faults
The upstairs cold water tank is more complex and can overflow for two different reasons:
1. Faulty Ballcock (Inlet Side)
If the ballcock inside the roof tank fails, the tank will overfill from the inlet. This is similar to the downstairs tank fault and is caused by:
- Worn internal seals
- Limescale buildup
- Float arm sticking or misaligned
2. Faulty Non-Return Valve (Outlet Side)
A faulty non-return valve can cause the tank to overfill from the outlet pipe. This happens when water is allowed to flow backwards into the tank instead of being held in the system.
This fault is common and often misunderstood, but it is a major cause of unexplained tank overflow.
Why the Water Pump Keeps Starting and Stopping
When either the ballcock or the non-return valve on the upstairs tank is faulty, it creates pressure loss in the system.
This causes the water pump to:
- Start and stop repeatedly
- Run for no obvious reason
- Wear out faster than it should
Many customers think the pump itself has failed, when in reality the problem is caused by a leaking valve allowing pressure to escape.
Professional Diagnosis and Replacement
I can quickly identify whether the issue is caused by a ballcock or a non-return valve and replace the faulty part using reliable components suitable for local water conditions.
Fixing the correct fault will:
- Stop the tank from overflowing
- Prevent water damage
- Stop unnecessary pump cycling
- Extend the life of your pump
Serving Lapta, Alsancak and Karsiyaka.
If your water tank is overflowing or your pump won’t stop starting, get in touch for a proper fix.
