Worcester Bosch 240 RSF Pressure problem

[montur]

Hello everyone me again. This time a combi as mentioned in the title.

The fault is when heating is turned on it runs for 10 minutes and then turns off the house hasnt warmed up yet pressure rises to 1.8 bar.

After looking at a few things i checked the expansion vessel it had very little air in and when the valve was pressed water came out which tells me the diaphram inside has perished.

It removed the tank full of water and drained it bits of rubber came out!

I got a replacement tank but it didnt fit in so am waiting for a replacement.

I reinstalled the vessel as DHW is needed but when the demand is made pressure jumps from 1 bar to just over 2 then thermal cutout happens and pump runs for a while trying to dissapate the heat.

Am i on the right track by changing the vessel?

Thanks

 

[Gasguru]

Depending on the air valve position on the expansion vessel it is sometimes possible for a small amount of water to be released from the vessel and it still to function ok. Set the air pressure to about 0.8 Bar with the boiler pressure on zero.

It appears you may have air trapped in the heat exchanger and the water is boiling causing a rapid increse in pressure and the o/heat stat to trip.

Isolate the gas and alternately run the heating and hot water in order to expel the air into the radiator circuit.

 

[montur]

thanks for the comment i will try that, there was a lot of water coming out of the vessel at the valve at one point it was dripping. i will try getting circulation through heater exchanger and let you know progress tomorrow. thanks

 

[montur]

Thanks Gasguru, the air was trapped in exchange because when i turned the HW tap on with gas off is came out in a few spurts and quite airy so that took care of that, now heating and water back to how it was.