I have been trying to fix this problem for nearly a year with no success. The heating works fine till it goes off and then within a minute the pressure drops to 0. We had someone out to service the boiler and said the expansion vessel was ok and it must be a leak...no signs of leak anywhere so we used an internal leak sealant... didn't work ..the radiators have been bled..don't know what else to do ..don't want to call another bloke out only to be told it's a leak nothing he can do again.
Is there anything else it can be? Can anyone help me get to the bottom of this?

ktc, December 2006

Thanks Stu I am going to try this. Last night, having turned off at mains, I topped up the system using the top up valve, to 1 bar..the pressure needle went up. This morning however, the needle had dropped back down to 0 bar though the system had been off all night.
Is this to be expected of a system needing repressurising?
Thanks for you help

ktc, December 2006

how do you pressurise an ideal classic boiler. pressure dropped when we bled the radiators don't kmnow how to get the pressure back up to 1 bar

gary hellewell, December 2006

open the prv by turning a quarter of a turn so it remains open.Attach a footpump to the valve on the red evpansion vessel.Pump up to about 1 bar.close prv by turning it again and refill boiler.job done

stu, December 2006

thanks stu for that.
Yes please could you tell me how to repressurise!
Thanks very much

Ktc, December 2006

Check the prv discharge point outside to see if its dry firstly.Then top the pressure up to 1 bar when the boiler is cold,turn it on and watch the pressure guage,if it starts to rise then its going to be the expansion vessel.It may only need repressurising.Can tell you how to do it if you need me to

stu, December 2006

had to have new prv as I kept topping up system too much to try and get more pressure..
could it be anything else?

ktc, December 2006

chech the prv not leaking

hi-spec, December 2006

I have been asking the same question! I have had this problem for over 5 years. I was convinced it was the boiler, just paid £2.700 for a new one and got the same problem! The only answer I get from my engineer is "You've got a leak" See my question Glowworm Flexicom 24cx

mrs millett, December 2006