Repairs & how-to
How to check a check valve (and foot valve)
A check valve (or non-return valve) is a simple one-way gate that stops water flowing backwards. On a pump drawing from a tank or well, the foot valve at the bottom of the suction line does the same job so the pump doesn’t lose its prime. When one fails you get short-cycling, lost prime, and a pump that seems to run for no reason.
What it does, and why a failure shows up
A check valve lets water pass one way and blocks it the other. If it leaks backwards, pressure bleeds away when the pump stops, so the pump kicks back on to top it up (short-cycling), or the suction line drains and the pump loses prime. So a bad valve often looks like a leak or a pump fault when it’s neither.
Signs of a failed valve
- The pump cycles on and off when no tap is open.
- The pump loses prime between uses.
- You can hear water draining back after the pump stops.
- Pressure falls away quickly once the pump shuts off.
How to check it
- Isolate the pump.
- With the system pressurised and all taps closed, watch the pressure. If it falls with no water being used, something is leaking back.
- Isolate sections one at a time (close a valve downstream of the check valve). If pressure now holds, the leak-back is upstream, the check or foot valve.
- On a removable in-line check valve, take it out and check the flap or ball seats cleanly and springs shut. Debris, wear, or a perished seat stops it sealing.
- A foot valve at the bottom of a suction line is harder to reach; if the pump loses prime and the above points to it, it’s usually the culprit.
Fixing it
Clean out any grit holding the valve open, or replace the valve if the flap, ball or seat is worn. Fit the replacement the right way round, they’re directional (there’s an arrow), and a backwards check valve blocks all flow.
Common questions
Check valve vs foot valve, what’s the difference?
Same idea, different spot. A foot valve sits at the very bottom of a suction line (in the tank or well) with a strainer, to keep the line primed. A check valve is an in-line one-way valve anywhere in the pipework. Many setups have both.
Which way does a check valve go?
In the direction of normal flow, there’s an arrow on the body. Fitted backwards it blocks the line completely, so always check the arrow.