Worcester 35 cdi II

[tedley]

Help ! I've got a Worcester 35 cdi II which seems to be ovepressurising when there is a demand. When cental heating is off and no demand for hot water, pressure is approx 1 bar. When c/h is on pressure rises to 3+ bar and water leaks from pressure relief valve at the rate of about a bucketful every couple of hours. I don't think this is normal. I have checked the expansion vessel and there is about 1 bar pressure. Anyone any ideas please? Thanks in advance

 

[keithkar]

Did you check the expansion vessel pressure after releasing system pressure ?

 

[tedley]

Thanks for response. Yes, system pressure was at 1 bar

 

[jackthom]

This sounds like a typical expansion vessel problem.

First it might be a good idea to check for a water leak in the vessel by unscrewing the nozzle and letting out a bit of air. If water comes out it's bad news.

Assuming no water comes out, to check the vessel pressure the system pressure must be reduced to zero on the gauge.

Then connect a foot pump and inflate the vessel to the pressure recommended by the boiler/vessel manufacturer.
Now re-pressure the system and fire up the boiler.

 

[tedley]

Thanks. Will give it a try and let you know outcome.

 

[tedley]

Tried releasing system pressure to zero, checked and adjusted expansion vessel pressure. I then re pressurised system to 1.5bar and fired it up. With central heating on, pressure rose to 3 bar at which time the pressure relief valve opened and a steady trickle of water comes from the overflow. I checked again after about ten minutes and the pressure had dropped to 2.5 bar and the dripping appears to have stopped. Any ideas why the pressure gets so high that the relief valve opens?