high pressure on combi boiler?

could be the filling loop letting by or hot water heat exchanger split.

chris gas
July 2008

Check the filling loop is'nt slightly open~if not then mains water could be passing in througt the hot water heat exchanger

Elvis
July 2008

if its rising with boiler switched off, it can only be filling loop passing even though it appears off, or pin holed heat exchanger allowing cold mains into system water and increasing pressure.

If you say its doing this when idle, not on, then make sure filling loop is closed and disconnect the hose after the isolation tap from the cold supply. you should have,

cold pipe
thumb tap or screw
flexible hose
(disconnect here)
non return valve
central heating pipe

if its allowing cold water to pass, it needs replaced.

please note advice is given based on pressure increasing even when boiler off

iain
July 2008