# thermostat backfeeding transformer



## xaH (Jun 21, 2013)

So you're an apprentice with an apprentice? :blink:


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## youngapprentice (Mar 31, 2012)

its just an old name im a jman at this point.


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## xaH (Jun 21, 2013)

As for your situation, both boilers and air handlers have their own 24 volt control power. If they are not isolated properly you can encounter a backfeed, but not with line voltage.


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## youngapprentice (Mar 31, 2012)

yeah it was backfeeding the transformer which then put out 120v cause transformers are fun like that.


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## xaH (Jun 21, 2013)

youngapprentice said:


> yeah it was backfeeding the transformer which then put out 120v cause transformers are fun like that.


Ahh ok, I got it now. :thumbsup:


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## Charlie K (Aug 14, 2008)

Check and see if there is a jumper between R and Rc on the thermostat. If it is jumped remove the jumper and check for backfeed.


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## xlink (Mar 12, 2012)

Charlie K said:


> Check and see if there is a jumper between R and Rc on the thermostat. If it is jumped remove the jumper and check for backfeed.


 Or, maybe some device is powering G in the air handler.


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