Overflow of the header tank with water room temperature

[bobinaki]

Hi all

My first post.

I have seen lately, at random times through the day, the header tank has been overflowing. The water leaking is room temperature and mosly transparent.
One thing I noticed is that the overflow immediately stops once I turn a hot water tap on. Also, one thing I tried is to turn off the boiler completely overnight but still had overflow.

Any ideas?

Thanks
Bob

[ericmark]

Ball valve needs adjusting or replacing.