Pressure relief valve to cylinder

[thehound]

Hello, on the feed pipe to my unvented electric hot water cylinder I have a Caleffi combined pressure reducing and pressure relief valve that is letting some water through constantly. I can hear it going to the overflow pipe.
It’s easy to access and I can source the replacement part.
I have read that it is most likely that the pressure relief valve has failed.

I live remotely so usually fix things myself if possible.

Do you think that’s the most likely fault?
I have turned the cold water supply down to reduce the pressure and that hasn’t sorted it.
Logically even if the cylinder or expansion tank were over pressured they wouldn’t cause this valve to open as it is a one way valve pointing from the fresh supply to the cylinder.

Would you agree?
And if the best plan of action is a straight swap, is it a case of isolating, draining off, swapping the part?
And then is it just a case of turning the water back on or will the expansion tank or cylinder have depressurised? I don’t have any equipment to check pressure.

I know cylinders can be dangerous so am keen not to make any stupid mistakes.

Thanks very much for any help.

 

[terryplumb]

You need a G3 certified plumber to do any work on an unvented cylinder, irrespective of how remotely you live.

 

[thehound]

You need a G3 certified plumber to do any work on an unvented cylinder, irrespective of you remotely you live.

Thanks I was wondering about that.
Do you think I could have caused any danger by just turning the cold supply off and on and whooshing some water through the valve? That’s all I’ve done so far so hopefully that’s ok!

 

[terryplumb]

Turning mains cold water down will not alter pressure ,but will reduce flow ,and isn't gonna cause any dangerous scenario's