Double check valve

[TonyKF]

I have recently had a leaking ball valve (fitted to the mains side of a closed system). As a temporary measure I connected up the flexible filling loop hoping it would at least stop water dripping out. Unfortunately, the pressure in the central heating system gradually started to rise even though the double check valve (heating side) was closed. I removed the filling loop and put a cap on the mains feed. This solved the problems - but how is it possible for mains water to enter the system with the double check valve closed? There is no pressure loss and no evidence of water dripping out of the valve or through the PRV. Is the double check valve also suspect?

 

[dextrous]

The double check valve did exactly what it is meant to do - it allows water in but not back out. There is no "closed" position involved- only the isolator valves will do this. Think you misunderstand the purpose of a double check valve.

 

[TonyKF]

Many thanks for your prompt reply. I assume, therefore, that the isolator valve (on the heating side of the double check valve unit) is faulty and that it is only the dc valve that's stopping water from coming out. Does this mean air could also get in?

 

[Agile]

Evidently I dont understand the original posting !

Whats a ball valve to do with a sealed and presurised heating system?

 

[keego]

They probably mean a ballofix valve.

 

[Agile]

On revisiting the OP I am sure thats whats meant.

But why shoule anyone go and buy a cap rather than a replacement ballofix valve?

I always replace screwdriver slot valves with plastic handle types now. So much easier and they rarely get left in the leaking position!

Some had a built in hysteresis to contribute to the problem.

Tony