Have you determined if the transformer has failed again? If so, list the screw terminals on the circuit board with thermostat wires connected - is "C" used? Does the system have a humidifier? We can probably ignore any possibility of any shorted line-voltage wires since the blower does run. Also, check the mounting of the circuit board. Dismount it and look for evidence of arcing against the enclosure. Assure that top edge of board is properly engaged in tabs on enclosure - they should alternate/stagger.

Yes, the transformer did fail again based on testing the line/load terminals.

Screw terminal C is used for one of the thermostat wires. Why do you suspect terminal C has something to do with things?

The system does not have a humidifier.

I'll check the board.

If the "C" terminal/wire was unused, it could not cause the transformer to overload. Even if the wire or thermostat was shorted, it could only cause the heat to operate continuously. Thus, that door remains open...

KC13 in doing a great job in trying to help you get to the bottom of your problem. But I would like to ask one question. Since the transformer is bad which side is bad the high voltage wiring or the low voltage wiring.

Don't get me wrong letmetellu... I'm appreciative of KC13's responses. I was just asking the question to expand my knowledge, not to question the legitimacy of the response.

The line side (Low Voltage) went bad.

The parts guy told me to install a 3A blade fuse in between the load and the transformer, to protect the transformer from burning out again. Works fine now.

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Originally Posted by spinn

Don't get me wrong letmetellu...I'm appreciative of KC13's responses. I was just asking the question to expand my knowledge, not to question the legitimacy of the response..

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I got that...

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Originally Posted by spinn

The line side (Low Voltage) went bad..

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Line (primary) side is line voltage, load (secondary) is low voltage.

Quote:

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Originally Posted by spinn

The parts guy told me to install a 3A blade fuse in between the load and the transformer, to protect the transformer from burning out again. Works fine now.

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That restores your control power, but what caused the old transformer to overload and/or fail? Fuses are cheaper than transformers, so that's still progress.