safety valve discharge

[uk_ducati]

hi
i have been called out to fix a sime friendly format 80e combi boiler. the problem is the presure gauge is at about 4 bar and there is water comming from the presure relief valve pipe whilst cold. i have narrowed it to the dhw heat exchanger leaking into the primary circuit. the problem is that when i isolate the cold water to the boiler the pressure drops but keeps on dropping to 0 bar. i would have thought that it would stay at 3 bar when the presure relief valve closes. Is this correct of is there a fault with the presure relief valve aswell

any advice would be welcome

cheers
paul

[htg engineer]

With the cold water turned off is there still water coming from the PRV ? If the pressure relief valve reaches 4 bar, it'll dump enough water to take the gauge to 0.

htg

[uk_ducati]

Hi
yes water still comes out of the PRV when the water is turned off. It keeps on discharging until the gauge reads 0 bar. What I am wondering is if the PRV is stuck open as I think this has been happening for a while judging by the state of the wall where the water hit it
I might just put a new one on whilst the system is drained to be sure
Am I in the right ball park with me thinking it is the DHW heat exchanger. I have checked the filling loop and that is fine

cheers
Paul

[htg engineer]

Turn off the cold water to the boiler, and run the heating, if the pressure doesn't rise to 4bar, then yes change the plate heat-ex.

And yes, I would also change the PRV.


htg

[uk_ducati]

hi

thanks for the tip but i cant run the heating as the PRV lets water through till the gauge reads 0 bar thus stopping the boiler from firing.
i will change the heat ex and the prv and will let you know how i get on

cheers

paul

[uk_ducati]

hi

managed to do it with replacing the PRV and DHW heat exchanger.

both had rusted

cheers for the advice HTG

paul