Unvented Cylinder

[ozzy]

Hi all hope you have all had a good Christmas and new year.
I have a customer with water running through the tundish. The PRV has been replaced but the water still runs through. The water is not hot so I don't believe its from the TPRV. The cylinder has a expansion vessel screwed in to the top. I checked the pressure and there was no reading. I pumped it up but the water is still going through the dish and the pressure has gone down. Could the vessel be the problem and needs replacing ? I do have a ticket for unvented as there are more of them about now but I haven't done many and would like your advice and help.
Thanks

 

[paulusgg]

I had something similar not so long ago, replaced the expansion vessel, the T&PRV but still had water running through the tundish. In the end I discovered a shower valve was allowing cold to feed back through the hot pipe work into the cylinder and then discharging. Ensure all mixer taps and shower valves have non return valves and the problem should go away

 

[Tonycane]

Pump up the vessel then spray some odd on the valve to see if the cores passing air?

 

[ozzy]

Thanks Paulusgg and Tonycane Will check them.

 

[stevetheplumber]

is the cold supply balanced if not this will back feed from any mixerswhen they are open of a shower all the time if premixed

 

[kay-jay]

It could still be the vessel. If it's losing its charge it's also losing the volume required for expansion.

 

[ozzy]

Thanks everyone for your help with this, its all sorted. The expansion vessel was shot and losing pressure and discharging back through the PRV. It had cut a grove in the seating and still ran after the vessel. Found the TPRV was not opening so its had a good service. New vessel, T&PRV. Thanks again.

 

[ShaunCorbs]

hope you didnt replace them yourself