Testing Boiler Pressure Vessel

[pallys]

Hi need some help.

Been having a problem where my worcestor bosch greenstar condensing system boiler the pressure would increase to 3bar and the PRV would open...

Pressed the schrader valve and only air came out, pressure was low though not much air in it. Drained the boiler then increased pv pressure to 0.9bar. Now the pressure guage on the boiler also increased at the same time, is that normal? or does it indicate the vessel is still faulty?

Thanks.

 

[Burnerman]

Others will know better, but its best to pressurise the EV when the rest of the system is completely depressurised....even disconnecting the thing if possible.
John

 

[Gasop]

Whatever you opened to drain the boiler then keep that open
whilst you recharge vessel.

 

[pallys]

The boiler was isolated from water by closing the inlet/outlet and drained of water via the PRV.

 

[Agile]

In spite of the guidance on this forum you don't seem to have read ANY of the FAQ/WICKI help.

That tells you NOT to drain via the PRV!

It also tells you how to repressurise the EXV properly.

I would love to rewrite it as it could be easier to follow but that would need to help of those with editing rights!

Tony

 

[pallys]

In spite of the guidance on this forum you don't seem to have read ANY of the FAQ/WICKI help.

That tells you NOT to drain via the PRV!

It also tells you how to repressurise the EXV properly.

I would love to rewrite it as it could be easier to follow but that would need to help of those with editing rights!

Tony

Hi Tony, I did read it, I used the PRV because it's already been blowing off since January when I spotted the pressure drops. Although I can isolate the boiler flow/return I haven't figured out how else to drain it.

I think the only thing thats not clear from your FAQ is that some form of draining must be open while pressuring the vessel, which probably explains why my boiler gauge increases as you recharge the vessel.

 

[Agile]

I did not write that FAQ ( and would like to rewrite it! ).

If you follow the instruction sequentially then you will be repressurising it with the system open to atmosphere!

Its meant to be an idiots guide do just do the job and is not intended for those who want to do their own ( wrong ) thinking!

Tony

 

[bazdaman]

What model worcester? The si and ri have drain points on boiler on right hand side

 

[ianmcd]

you are doing it wrong the boiler pressure guage should not rise as you re-charge the vessel, you MUST leave a path for water trapped in the expansion vessel to be drained , as you say your PRV is suspect now anyway so just make sure that it is open as you re charge the air in the vessel, dont recharge it too high as this can be just as bad, manually open and close the prv a few times before filling the boiler with water, this is the ONLY way this can be done

 

[pallys]

Hi guys,

5 years later and this has happened to me again - have lost pressure in the expansion vessel and PRV released water (now leaking slightly which I hopefully settled like last time).

Vessel had tiny amount of air come out - no water.

So I need to pressurise the vessel again:

- boiler switched off
- have isolated the boiler by closing the 2 valves under the boiler for CH flow and CH return.
- filling loop from cold main feed closed.
- boiler drained via the drain point under boiler (see lower far left on pic attached).
- boiler gauge needle now on 0
- left drain point open
- pressurised vessel to 0.75 bar as per spec but the boilers water pressure gauge increases as I do this.

Am I doing this wrong as I didn't expect the boiler gauge to increase from zero as I pressurised vessel?

I'm finding the FAQ guidence on vessel recharge confusing (it's not clear enough to be a sticky) - so if anyone has any clearer instructions would be much appreciated because there seems to be all sorts of guidance out there, isolate boiler, don't isolate boiler etc.

Boiler is Worcester ZB 7-28 HE System.

Thanks.

 

[pallys]

So I drained as much as I could with boiler isolated via drain cock near boiler.
I used the PRV to check if there was still water and there was so I drained the rest out via the PRV (I know I shouldn't do this but it was already leaky).
Pumped expansion vessel to 11psi (0.75 bar) and this time boiler pressure gauge did not move.
Closed drain cock and opened the isolation valves.
Topped up boiler to 1 bar.
Measured expansion vessel pressure and it was now showing 1.1 bar.

Is it to be expected topping up the boiler with water would also increase expansion vessel pressure? because I'm not sure if vessel is faulty and needs replacing.

 

[andytw]

I always replace the schraeder valve when doing this. Screws into the valve stem. Few pence from Halfords.

 

[Madrab]

As the system water pressure is raised to working pressure that will then compress the air in the vessel increasing its pressure, so yes the pressure in the vessel will rise.

Pre-charge the vessel to the recommended pressure as specified in the boiler MI and then leave it. Should be no reason to re-check it as doing so may release some of the air and dropping the pressure .

 

[ianmcd]

you need to leave the boiler isolation valves open when you are pressurising the vessel in your instance as the drain point is beyond the valves so where can the excess water go if the valves are closed, tip stop opening and closing isolation valves or they will leak

 

[pallys]

Thanks for your help.

So for reference for next time - as I'll forget what to do when it happens in 5 years time again:

1. Switch off boiler - (don't touch isolation valves i.e leave open)
2. Drain boiler via boiler drain point
3. Pressurise vessel to spec (0.75 bar / 11 psi) (boiler pressure gauge should not move, if it does then not enough water drained in boiler)
   
4. Close boiler drain point
   
5. Pressure boiler to 1 bar slowly
   
6. Switch on boiler

Please let me know if anything flawed in that process because I'm not sure approach is correct as approach slighty differs from sticky.

Thanks for help, much appreciated.