Swift combi boiler builds up pressure after a short while either firing or standing still . I have to release safety vave to ease pressure. Do I have to replace water pressure switch or the elecrical compoments what way Iam able to find out .Is it somthing else not related to what think it is.

frank, July 2008

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