Hi guys,
First - a big thanks to all your help - I changed both thermisters at the weekend, the problem seems to have gone away and the wife is happy!!
A slight issue is that to change the CH one, I had to drain the boiler through the PRV and now I can't get it to stop dripping. It's only about a single drop every 15 secs or so but it's enough to drop the pressure a bit over the course of a day.
Will this sort itself out after a few days or is there something I can do to help it seal up again? Also, I've read a few posts about leaking PRV being a sympton of a busted expanision vessel - I wouldn;t have busted it just by draining the boiler would I?
Thanks all.
Ben