CH only working when HW is on.

[Des Jennings]

Hi. In the last couple of days, my 2-year-old Worcester Bosch boiler has switched itself off and only switching the HW on will reignite the boiler and get the water circulating. Once the HW has reached temperature the boiler switches off and the radiators cool down. I reset the boiler today and it ignited but would only stay that way for a short time but once again switching on the HW worked for a while. I had the reverse situation last summer where the HW would only heat up if the CH was on. It turned out that the Honeywell motorised valve actuator needed replacing and everything was fine (surely the actuator hasn't failed already). I should add that the expansion tank next to the Heatrae Sadia cylinder is reading 0.2 bar and has been quite low for some time. At one point I suspected the Potterton EP2002 timer, but I'm not so sure now.

Help, please.

 

[CBW]

So I’m guessing you have an unvented cylinder? Top that pressure up firstly, and then see if that gets it working.

 

[Des Jennings]

Thanks. I do have an unvented cylinder. I should add that boiler, linked to CH only, has been working again for some time now. There doesn't appear to be a pattern to when the boiler might switch off.

 

[ianmcd]

you need to turn that pressure up

 

[Des Jennings]

I raised the pressure in the expansion tank to 1.0 bar on Wednesday morning and the boiler fired up ok and there have been no problems until tonight when I noticed that the boiler had cut out. Once again, by putting on the HW the CH was restored. Is this the heating valve causing problems? I should add the boiler fired up without my assistance just before the tank pressure was raised.

Thanks.