potterton pressure keeps going up, help please

[doppo189]

Hi people
Have just put new diverter on potterton puma 80, plus microswitch and pressure relive valve.

My problem now is when central heating on the pressure creeps up to over 3 bar, when heating not on lose all pressure and have to refill.
The flexi pipe is disconected so this is not leaking into boiler any help please as worried why the pressure goes up and also why the relive valve does not kick in???

 

[Elkato531]

The expansion vessel has probably lost its pre charge.
You can measure it with a tyre pressure gauge and re-pressurise it with a bike pump. Look in the MIs to find the required pressure. If it loses pressure again the diaphragm inside will be perforated and you need a new expansion vessel.

 

[doppo189]

Hi
Elkato 531

Thanks for reply and being so quick.

 

[Elkato531]

Extra thought.

If the expansion vessel does keep losing pressure, Check the schrader valve on it first before replacing vessel. Unlikely but much easier and cheaper.

 

[MANDATE]

When you re fill, what pressure are you refilling to.
When CH is on, the pressure should rise about 1 bar, say from 1.5 to 2.5 but it should not exceed the pressure relief valve setting.(3.5)
If the rise in pressure exceeds 1 bar by a significant amount and enough to operate the PRV, it suggests the expansion vessel is not performing.
Either the diaphram is punctured so water passes through to the air side, or it's lost its air pressure. So there is nowhere for the water to expand to.
When the PRV operates at 3.5 bar the pressure will drop basically to nil and it sounds as that is what is happening.

 

[doppo189]

Hi guys

Thanks for advice. Just one question is the schrader valve the little valve sticking out near top of boiler with a plastic tube connected.

Thanks again
Chris

 

[MANDATE]

The valve is on the expansion vessel.
It's just the same as the valve on a car tyre, or bicycle tyre. You can press the end of it to let out a bit of air if theres any in. If water comes out you'll need to replace the expansion vessel.
You'll need to follow the correct procedure of course.
Don't know about the plastic tube, Mine doesn't have any tube, but mine's a different boiler