Losing pressure.

5 Jan 2014
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United Kingdom
My Worcester Bosch 28 CDi combi boilers losing pressure. I tried re-pressurizing the expansion tank and re-filling. Pressure up to 1.5 Bar. When CH came on the pressure went up to about 1.9. Over the night time when the boiler goes of the pressure gauge slowly drops to almost nothing. Boiler still comes on in the morning and pressure goes up a little but not up to 1.0 bar.

Can't find any leaks.

Do I need to re- seat my PRV?

Any ideas anyone?

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Do I need to re- seat my PRV?

Any ideas anyone?


Does water come out of the pressure relief pipe? You can find out in dry weather (if you're lucky enough to find some) by putting a plastic bag over the end of the pipe overnight.
Sounds like you need a new PRV then as it is either leaking or lifting at too low a pressure. 1.9 bar should not lift it. You'll hardly ever get a PRV to re-seal once it is leaking. It might be worth checking the expansion vessel pressure at the same time. Somewhere in the wiki or the faq's there are instructions on how to do this.
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Ok thanks.
I did re -pressurize the expansion vessel as it was flat.
Sounds like I need a new relief valve.
Indeed, new PRV.

Probably what's happened if the EXV was flat is that it's gone above 3 bar, PRV has lifted and crud has got in, and they don't reseal again afterward. Don't use the test lever/knob either!
When I had probs I did turn the knob around to see if it let pressure or water out.
New one it is then

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