DHW working but CH causes gas valve to shut on Glowworm

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Glowworm swiftflow 100 boiler. I have replaced the PCB and the DHW side is now working fine but when the CH is switched on the burner stays on no longer than 40 mins from cold. Less if it has recently been on. The gas valve just shuts off completely. It also doesn't look as if the burner is modulating even on DHW when the flow from tap is adjusted.

Any ideas before I start replacing CH thermister? etc :confused:
 
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Theres 4 of them right - 2 for DHW and CH temp and 2 for DHW and CH gas pressure?

Which ones should I be looking at ?
 
Actually to blunt - I do know where they are but haven't the foggeist idea of how to go about setting them. Its certainly not covered in the installer instructions. :cry:
 
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You need at least a manometer to set the minimum and maximum gas pressures that the valve will modulate between...if the minimum gas rate is set too low the boiler will simply go out and too high will start sooting up and blocking the heat exchanger.
 
ollski said:
You need at least a manometer to set the minimum and maximum gas pressures that the valve will modulate between...if the minimum gas rate is set too low the boiler will simply go out and too high will start sooting up and blocking the heat exchanger.

I take it then if I attach a U gauge and measure the burner pressure with a call for gas and then alter the potentionmeters this will alter the burner pressure to what is required for CH and DHW?

Oh and thanks for the pointer :D
 
No joy on with the potentiometersI'm afraid. The CH pressure is about 1.5bar. When it is turned on it goes over 3 bar and then the gas valve shuts . I stood theit and timed it and it was around 25 mins.
 
Have you measured any temperatures?

How hot is it getting when it knocks off?
 
Very hot - lol .There is no to little difference in the temp of the flow and return pipes. I haven't actually measured them but thats by touch. All rads are getting blazing hot - too hot to touch really.
 
Also there is no modulation , I had a u gauge on and even on the DHW the burner was either on or off.
 

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