Cold water tank fills with hot, then overflows

[jeff the gasman]

It's not rocket science.
Isolate every hot pipe that attaches to any mixer. If it stops which it will you only have to open them one at a time to find the culprit.
It HAS to be where hot meets cold and is simply a process off elimination.
Jeff

 

[jeff the gasman]

Could cause problems if not seating correctly.
Jeff

 

[JackHennety]

I appreciate it isn't rocket science. But the reason I'm asking all this stuff is because you know considerably more about it than I do.

I know it's a process of elimination, so could you confirm that if non-return valves have been fitted to a mixer then that eliminates that mixer from the equation, assuming they're correctly fitted?

 

[jeff the gasman]

Yes and assuming they are not made in a chinese labour camp and faulty.
A lot of imports are of a very poor quality.
Jeff

 

[JackHennety]

Ok, thanks Jeff.

 

[JackHennety]

Just for the benefit of anyone else who has this problem, it did indeed turn out to be mixer tap related - and in fact it was more than one mixer that was the problem.

I hadn't troubleshot it properly in the first place because I had tried to isolate the mixer causing the problem by turning them off one by one. This didn't work - no matter which one was turned off it kept overflowing. But then I turned off the supply to all of the mixers at once and turned them back on by one. This revealed that two of the mixers were responsible (kitchen tap and en-suite shower). After fitting non-return valves to both of those mixers, the problem was solved.

I still don't understand why it should have started happening simply as a result of the water being turned on and off a few times, with no change to any of the taps, but it did.

Thanks to Jeff and all who replied. You were right!

 

[jeff the gasman]

Thanks for the feed back much appreciated.
Jeff