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Post by Mark on Mar 16, 2013 2:14:45 GMT -5
Hi,
I am a gas engineer and have never came across this fault with a Powermax 155x before. The boiler locks out after 3 ignition attempts, however whilst the fan is running, there is a gurgling sound almost like water circulation, but only when the fan runs. As the appliance is a thermal store, during this stage in the sequence the ch/hw pumps remain still, so it seems like there is a bad combination of water in the flue way?
Regards
Mark
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Post by northpole on Mar 16, 2013 5:16:23 GMT -5
Mark,
See my response to your post in the General section.
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Post by Dave on Apr 4, 2013 13:45:57 GMT -5
hi My top left limit thermostat switch needs manually resetting about 4 or 5 times a week - any ideas of what the problem could be before i get an engineer out?
any advice is appreciated:)
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Post by Mike the Boilerman on Apr 5, 2013 3:17:18 GMT -5
Dave,
This is usually caused by the 'hold off relay' failing. Part number P759. I suggest you test yours and replace it if not working. Or just replace it anyway if you aren't sure about how to test it's operation. They are not expensive. Google the part number, plus the word Powermax.
Mike
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Post by northpole on Apr 7, 2013 8:04:56 GMT -5
Mike,
Just for information, could you explain what the 'hold off relay' does and how it interacts with the limit stat.? - I assume this is Item Key no. 91 on page 19 of the Powermax 155x Service Manual, but I can't identify it on the functional diagram on page 13. I have had problems similar to Dave in the past, but my engineer has never mentioned this relay as a possible cause.
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Post by steve on Apr 7, 2013 16:57:22 GMT -5
hi northpole
I think the relay you are talking about item 91 on page 13 is the relay above the limit switch (top left of boiler), I think this may be the relay shown on the schematic as the pump relay. Hopefully Mike having more knowledge can explain how it interacts with the limit stat.
But as a guest it probably keeps pump running longer so that the water in the heat exchanger circulates and if this fails the limit stat trips?. Although i'm still confused over function of the 2 different stats - limit and overtemp stats. Hopefully mike can explain to help both of us.
Steve
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Post by Mike the Boilerman on Apr 8, 2013 17:27:12 GMT -5
Steve is correct, it is at the top left hand corner of the panel inside. It makes the DHW pump run while the burners are alight in order to mix up the water in the tanks and prevent temperature stratification. When the relay fails, the pump doesn't run and the top of the boiler gets far hotter than the middle where the control thermostat sensor is, leading to the overheat stat (sensor at the top) tripping.
Mike
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Post by northpole on Apr 20, 2013 5:30:23 GMT -5
Mike,
Assuming that the relay is working and the DHW pump does run while the burner is lit, are there any other reasons you can suggest why the limit stat. should trip? (which I assume means that temperature stratification is nonetheless occurring and the water at the top of the tank is becoming too hot).
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Post by Mike the Boilerman on Apr 26, 2013 7:01:55 GMT -5
Bit of an unlikely situation you outline, but the overheat stat would trip if the main control stat was failing. This would not lead to stratification, rather the whole thermal store getting up to 90 degrees C approx. Or might happen if the pump impeller was bunged up with crud (but then the HW wouldn't work either). I can't think of any other reasons.
Mike
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Post by northpole on Apr 27, 2013 5:06:44 GMT -5
Thanks Mike - I had trouble last year with the limit stat. on my 155x tripping regularly, even though it had been replaced three times and the boiler stat. twice for this very reason! As the DHW pump (which is not the original one AFAIK - it's a Grundfos single speed model) did appear to be running when the burner was lit, I was just wondering if there might have been other potential causes of overheating that you could suggest.
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Post by Mike the Boilerman on Apr 30, 2013 13:43:44 GMT -5
Thanks Mike - I had trouble last year with the limit stat. on my 155x tripping regularly, even though it had been replaced three times and the boiler stat. twice for this very reason! As the DHW pump (which is not the original one AFAIK - it's a Grundfos single speed model) did appear to be running when the burner was lit, I was just wondering if there might have been other potential causes of overheating that you could suggest. Hmmm that's really odd. I can't explain that. Provided the DHW pump runs while the burner is alight, I think the work-around fix would be to adjust the boiler stat down a little. There is a spindle on it for this, but no knob attached to discourage technicians form fiddling with it! Mike
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Post by Steve on Jun 29, 2013 15:14:46 GMT -5
Hi Mike Thanks for all the very useful info on this site I have been using it to try to resolve a problem with the top left stat that keeps tripping out. I've renewed the pump relay but stat still trips out on a daily bases. The pump sounds as though its running ok - Is it possible to check without dismantling any pipes to save the hassle of draining the tank if the shut off valves do not hold. Also if I find the pump is running what could I look at next? You also mention on some threads that the boiler stat could fail could this be a cause and how would I check or change or could I adjust down to a lower temperature?
Once again many thanks for all the info on this site it has given me some understanding of how the boiler works
Steve
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Post by Steve on Jun 29, 2013 15:15:52 GMT -5
Hi Mike
Thanks for all the very useful info on this site I have been using it to try to resolve a problem with the top left stat that keeps tripping out. I've renewed the pump relay but stat still trips out on a daily bases. The pump sounds as though its running ok - Is it possible to check without dismantling any pipes to save the hassle of draining the tank if the shut off valves do not hold.
Also if I find the pump is running what could I look at next?
You also mention on some threads that the boiler stat could fail could this be a cause and how would I check or change or could I adjust down to a lower temperature?
Once again many thanks for all the info on this site it has given me some understanding of how the boiler works
Steve
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Post by Steve on Jul 4, 2013 10:35:52 GMT -5
Looking at the problem again I found the below which I thought I should share incase it helps others:-
When the boiler is running and I turn down the boiler stat spindle then the pump stops so assume the boiler stat is ok?.(this also proves the pump relay is switching ok!)
Also if I draw off hot water then the pump starts ok so assume the flow relay is ok?
Assume the pump is pumping water ok as pump bottom pipe is hot when running?
Could it be that the boiler stat was stuck and when I turned spindle it freed itself so it may be ok?
I've since left it just down slightly to see if this stops the left stat tripping.
Mike Not sure above is right or helpful but now at a lost if it trips again :(
Steve
Steve
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Post by northpole on Nov 20, 2013 11:32:01 GMT -5
Thanks Mike - I had trouble last year with the limit stat. on my 155x tripping regularly, even though it had been replaced three times and the boiler stat. twice for this very reason! As the DHW pump (which is not the original one AFAIK - it's a Grundfos single speed model) did appear to be running when the burner was lit, I was just wondering if there might have been other potential causes of overheating that you could suggest. Hmmm that's really odd. I can't explain that. Provided the DHW pump runs while the burner is alight, I think the work-around fix would be to adjust the boiler stat down a little. There is a spindle on it for this, but no knob attached to discourage technicians form fiddling with it! Mike Mike, For some reason I missed your response at the time - this is the very fix my own engineer eventually suggested. I have found about one-eighth anti-clockwise turn of the spindle from the maximum position seems to do the trick. Just worried though in case there might be long-term adverse effects - am I worrying unnecessarily?
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