header tank overflow problem.

[madsey]

I have a indirect combination cylinder in the attic and the cold water header tank keeps overflowing.
I've changed ball valve but this has not cured the problem.
When i draw hot water out of the hot water tank,the level in the cold water header tank returns to normal but within about 24-48 hrs the water level has risen agian and overflowing.

The cold water tank overflows even when the central heating is not on.

The ball valve is not leaking at all.

Im thinking it might be a hole in the coil inside the hot water tank.

Thanks for any help.

 

[45yearsagasman]

Where is the ch header tank in relation to the combination cylinder?

 

[madsey]

Hi, It's about 12'' to 18'' above the cold water header tank.

Thanks,madsey.

 

[45yearsagasman]

It could well be then a failed coil. Is it possible to temporarily isolate the cold feed from the header tank? That will prove or not wether the coil has failed.

 

[Whitespirit66]

If you have mixer taps, could be mains pressure from cold side backfeeding into hot side and adding to tank level.

 

[madsey]

Thanks for your replies.
How do isolate the ch header tank to test if my coil does have a hole in it ???

Also,i do have mixer taps but they have been in the house since the hot water tank was installed 8 yrs ago.

Thanks again for your help.