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Challenger cc125 temp spike

Paul_69 Member Posts: 251
When running hot water only the heat temp gauge shoots up to 250 degrees but he setting is set at 140 and the boiler overheats and starts steaming and banging flow check. No problem when running heat only. Dirty heat exchanger on domestic side? Dhw sensor? I clean flow sensor. Thx


  • kcopp
    kcopp Member Posts: 4,187
    edited January 2016
    Sounds like the flow sensor.
    I had to service that last year in that very model.
    It is not a hard fix.
    They don't like to be cleaned. Just replace it.
    What is your water like? Well water or City? Hard? The coil that goes through that unit is pretty small.
    One of the things I like about that unit is that there are very few parts to replace.
  • Paul_69
    Paul_69 Member Posts: 251
    They have dirty water,how can it be flow sensor that just turns on burner when water is flowing,if that was issue wouldn't that do it when water is not flowing?thx
  • kcopp
    kcopp Member Posts: 4,187
    edited January 2016
    What is the flow like?
    What is the incoming water temp and the outgoing?
    is there a mixing valve on the domestic piping?
    I replaced the water pressure sensor.
    If the water quality is poor you need to address that.... asap