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Ferroli sigma 60-100 only works when thermostat disconnected and reconnected

Discussion in 'Plumbing and Central Heating' started by Jock_Meyer, 12 Oct 2021.

  1. Jock_Meyer


    12 Oct 2021
    Thanks Received:
    United Kingdom
    Morning everyone.

    I've got a problem on a ferroli sigma 60-100 and was wondering if anyone could share some hindsight.

    On demand of CH+HW or any of them the pump runs, but boiler doesn't start.
    Main PCB and gas valve PCB were sent away for testing and all came back good.

    Replaced safety thermostat, Venturi fan casings, pressure switch works ok, checked electrode all good.
    Got two different temp sensors delivered, one silver and one gold both with different resistance values but both ordered as compatible with the ferroli sigma 69-100.

    Now with the gold temp sensor connected the boiler doesn't work no matter what.
    With the silver one, when CH or HW on if I disconnect one of the thermostat legs, the fan runs + can hear electrode sparking and once I connect the thermostat leg back in the boiler then fires no problem and runs fine until has to be started again which the it's a case of disconnecting and reconnecting the thermostat again to get it running.

    Any help appreciated

    Attached Files:

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