Pressure increasing even when not used - looks like cold water feed

[Johnxhamilton]

Daughter's boiler, Alpha CB28, increases in pressure to the point the pressure release valve is kicking in. This is even when it's not being used (unoccupied flat), and can rise from 1.5 bar to 3.5 overnight!

Boiler works fine for both heating and hot water otherwise.

i have eliminated it being the pressure fill circuit as I've switched it off at both ends. However, When I switch off the cold water feed (for the hot water) - pressure is fine after the usual few hours delay.

is it likely to be heat exchanger or diversion valve?

 

[Dotty]

It's likely to require a visit from a qualified gsr.

Call one in. Or put a post up here - [DLMURL="http://www.ukplumbersforums.co.uk/im-looking-plumber-gas-engineer/"]I'm looking for a Plumber or Gas Engineer[/DLMURL]

And this is where the thread ends.