Worcester-bosch 254si (I think) combi-boiler. The pressure increases to 3.5bar within 24 hours. The inlet valve has been replaced with no effect.

john, June 2007

possibly expansion vessel has worn out,possibly outside the boiler at the rear,remove dust cap,same type fitting as bicycle tyre,push pin with small nail or small flat head screwdriver,should be small burst of air,if water squirts out,expansion vessel will need replacing or drained and can be repressurised using foot pump or similar.

Impressive heating., July 2007

hi-spec is correct -the only way your heating system can increase in pressure (assuming the system is plumbed correctly) is through the domestic water heat exchanger which is known as a "plate heat exchanger"

Never heard of one failing before but I suppose it is possible.
they as made of stainless steel and generally have 4 connections -2 for the primary water and 2 for the domestic

do remove filling loop as hi-spec suggests - it is possible for these to pass water

dave b

dave broadbent, June 2007

Thank you very much

john, June 2007

if you've checked your filling loop is ok and not letting by but your pressure is still rising its your dhw heat exchanger faulty and passing water from your dhw (domestic hot water) to the primary circult (heating side)
to stop it till you can fit a new heat exchanger isolate your main stopcock.

hi-spec plumbing, June 2007

yes, it rises to 3.5 bar when the heating is not on.

john, June 2007

is it at 3.5 bar all the time without the heating swiched on

hi-spec plumbing, June 2007