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Glow Worm Combi hot water

Hi All, I have a problem with my Glow worm Swiftflow 80, when I turn on the hot tap the boiler fires up but only for a few seconds then the gas shuts off, the pilot light stays lit. The central heating works OK, the gas remains lit when it is turned on, this (in my mind) rules out a problem with the fan. I initially thought it was the water pressure switch so I replaced it, then after reading some previous posts I thought it could be the HW thermistor but neither of these things worked. The water pressure switch is adjustable where the original had a fixed sensitivity, I have not tried adjusting the screw, I just installed it as it came. Any ideas as to what to try next ? Regards Alan

Reply to
Maymo
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Have you monitored the water flow switch? Does the pump operate OK?

Reply to
Ed Sirett

The pump seems to be fine, I have just tried the CH for 10 minutes and it is all working great. While the CH was on I tried the hot tap and the water heated up, then went cold then hot again and carried on like this switching every 30 seconds or so. Why would the pump make any difference to the DHW, surely the DHW would work even if the CH pump didn't? How do I monitor the water flow switch, I have a multimeter. Now that the CH is off the DHW is still cycling hot and cold, the system is still warm. Alan

Reply to
Maymo

When you run a HW tap without switching the CH on does the water run cold-hot-cold-hot? Or does the boiler fire for 10 seconds and never again?

I'm beginning to think you have a problem with a scaled up secondary heat exchanger.

Reply to
Ed Sirett

On closer inspection I now think that the gas is not firing up at all, the CH has been off all day, I open the hot tap and cold water comes out shortly followed by tepid water for 10 seconds then cold water continuously. The boiler makes a noise when the tap is open which I thought was the gas but now I have doubts, perhaps its just the sound of the water flowing through the system.

I have a manual for the boiler and I can't find a secondary heat exchanger, does it have one?

Do I check the voltage of the flow switch with the multimeter in series? what voltage should I expect when the tap is shut and open?

Thanks for your help. Alan

Reply to
Maymo

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