I suppose that is a possibility, but it doesn't seem to happen if not used for long periods during the day.
Will double check it though! thanks for replying so quickly.
I feel guilty about registering just to post and ask a question but hopefully someone can provide some help.
We have an immersion boiler which does hot water only. It is fed from the water tank which sits about 2 feet above it.
Our heating system is a seperate back boiler wood burner...