Hi Domenic,

I replaced a johnson control thermostat a-19 for a sunstat dial #500710 four years ago

for a heated floor.  Now just noticed connection and black wire behind sunstat burned and melted, what could be the cause?    Thanks for your time.

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Lucio 4 years 1 Answer 548 views 0

Answer ( 1 )

  1. Being that is was working for years it could really be a few things.

    The first thing comes to mind is a bad connection. A bad connection will cause a high resistance and would get hot. Or you’ve bigger issues. Your transformer could be malfunctioning and putting out more than the 24 volts needed.

    First I would put a tester on your transformer and look for 24 volts AC.

    I mean, was the system working? how did you noticed it was melted?


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