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Likely Gas Combi-Boiler P.C.B. Damage.

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Mornin' all,

                         I hope that you are all keeping your spirits up during these trying times.


Yesterday I made a mistake. I can only attribute the reason to the work environment and me being pre-occupied with self distancing on site and being distracted by the house occupants, plus stupidity.


The owner had apparently struck a wall thermostat due to it being unreliable in operation, and he having a bad temper. The dial part was cracked. He asked me to change it for a new one. The wall thermostat is a Honeywell make. I have wired up many of these in my time. I did not have a Honeywell replacement but did have another make of a similar design. So I fitted that. After I had fitted the new one I noticed that I had no mains supply showing at the wall stat. I checked the switched fused connection unit at the boiler and it was displaying a glowing neon, so the 3 Amp fuse there was intact. I was asked to refit the original wall stat, which I did, and a gas engineer is coming out to look at the boiler. I did not see the boiler working initially, but the owner and his wife assured me that it was working that morning.


I must have wired the new wall stat up wrongly and shorted between L and N. That probably blew the 1, 2 or 3.15 Amp fuse on the boiler P.C.B. I did not dismantle the boiler to look.


What is the chance of irreparable damage to the boiler P.C.B?


Unfortunately I did not note the make and model of the boiler.


Bye,


Gloomy Z.

  • 0
    No more than that due to the customers deliberate damage to the original thermostat.


    Is that the answer you want ?
  • 0
    I would be a little surprised if the fuse in the boiler had gone and not taken out the 3a in the spur too.

    Also maybe the thermostat isn’t switching 230, it could be low voltage? I nearly got caught out by one of those last year...
  • 0

    Sparkymark:

    I would be a little surprised if the fuse in the boiler had gone and not taken out the 3a in the spur too.

    Also maybe the thermostat isn’t switching 230, it could be low voltage? I nearly got caught out by one of those last year...




    That is a good point. It might have been an extra low Voltage control circuit. But that would not have accounted for the lack of life at the boiler would it? I tested at the room stat position and my tester showed no supply at all, and it reads down to 6 Volts A.C. and D.C. The boiler was not doing anything at all. Showing no lights or display readout. Perhaps the boiler was faulty before I arrived, or it has an intermittent fault. Was the customer just trying to eliminate the room stat from the equation? The old room stat was definitely faulty as I tested it. It worked after a fashion but not reliably.


    Z.

  • 0

    Sparkingchip:

    No more than that due to the customers deliberate damage to the original thermostat.


    Is that the answer you want ?




    Anything to cheer me up. Thanks Andy.


    Z.

  • 0
    The mains voltage thermostats have a heater resistor in them to provide hysteresis, and behave rather oddly when just powered up (had one last week). If the boiler expected a LV electronic one I expect that it would not work at all. I doubt that you have damaged anything, its just one of those things, and may not have worked correctly for some time (thus the "thumping the thermostat"). I doubt that there is an additional fuse in the boiler.
  • 0

    Sparkymark:

    I would be a little surprised if the fuse in the boiler had gone and not taken out the 3a in the spur too. . . 




    Not convinced about that. I came across a boiler that had received too many volts a few years ago due to a wiring error. All that was left of the first fuse in the boiler was it’s endcaps - the pc mounted fuse holder had even been blown out of shape. The 3A fuse in the fused spur was still sound. 


    Regards,


    Alan. 

  • 0

    davezawadi:

    The mains voltage thermostats have a heater resistor in them to provide hysteresis, and behave rather oddly when just powered up (had one last week). If the boiler expected a LV electronic one I expect that it would not work at all. I doubt that you have damaged anything, its just one of those things, and may not have worked correctly for some time (thus the "thumping the thermostat"). I doubt that there is an additional fuse in the boiler.




    Yes, definitely a mains rated wall stat with a heater resistor inside connected to N.


    Z.

  • 0

    Alan Capon:




    Sparkymark:

    I would be a little surprised if the fuse in the boiler had gone and not taken out the 3a in the spur too. . . 




    Not convinced about that. I came across a boiler that had received too many volts a few years ago due to a wiring error. All that was left of the first fuse in the boiler was it’s endcaps - the pc mounted fuse holder had even been blown out of shape. The 3A fuse in the fused spur was still sound. 


    Regards,


    Alan. 


     




    Oh ek!


    Z.

  • 0
    Hang on!


    Isn't the thermostat just a temperature controlled switch? Does it have any significant resistance when the contacts are closed?
  • 0

    Chris Pearson:

    Hang on!


    Isn't the thermostat just a temperature controlled switch? Does it have any significant resistance when the contacts are closed?




    The old faulty one did. The new one should have just minimal contact resistance. What's your point Chris?


    Z.


     

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