central heating problem

[Rollin]

We have just moved into a house that has a glow worm combi boiler. The hot water side of things is fine, but we can't get the central heating to work.

What happens is as follows.

1. I can set the desired temperature.
2. Boiler fires up.
3. Display shows temperature rising to desired figure (takes a few seconds)
4. Boiler then seems to power down.
5. The pipe leading to radiators is hot near boiler but cold about a foot away.

A friend suggested that the pump maybe stuck since CH might not have been used for a bit. The pump seems to be operating fine though as I can alter its speed with a switch and it responds.

Boiler is only 1.5 years old. Anyone have any ideas what's wrong?

[mfmman]

Diverting valve stuck, if you run a hot tap does the boiler fire and stay on (with the hot tap still ruuning hot)?

[Cas_P]

Have you looked at the boiler itself? what pressure is it at? I had this problem, the pressure was too low so I had to open the valve for a bit to get the pressure up and it worked fine after that .

[Rollin]

mfmman said:

Diverting valve stuck, if you run a hot tap does the boiler fire and stay on (with the hot tap still ruuning hot)?

Boiler fires up when I turn hot water on and a flame symbol appears on the display. The tap still runs hot.

Can I fix diverting valve myself?

[Rollin]

Cas_P said:

Have you looked at the boiler itself? what pressure is it at? I had this problem, the pressure was too low so I had to open the valve for a bit to get the pressure up and it worked fine after that .

Pressure is fine, 1.5 bar.

[mfmman]

Rollin said:

mfmman said:

Diverting valve stuck, if you run a hot tap does the boiler fire and stay on (with the hot tap still ruuning hot)?

Boiler fires up when I turn hot water on and a flame symbol appears on the display. The tap still runs hot.

Can I fix diverting valve myself?

If you mean legally than yes I believe you can, however domestic regs are not my thing so you must check. It might be a bit more complex than my suggestion mind but it is a good starting point. Does your boiler have the ability to have the hot water completely off and the heating on. If you can do this and the boiler fires and hot water comes out when the hot water is off then I think it must be the valve

[Rollin]

I've gone into the diagnostic menu on the boiler. It says everything is working fine...

[dirkgently]

Make and model of the boiler?

[Rollin]

Glow worm ultracom 38 cxi

[dirkgently]

Ether the diverter valve is not changing over or the automatic by-pass valve is stuck open.
Can you feel if the plate heat exchanger is getting hot with no hot water demand?