Hi, while changing my old thermostat to a new one I
didn't realize I had the wrong circuit breaker tripped
in my home. Turns out that the new thermostat is not
compatible to the wiring in my house(I think) and
after hook up there was no power to the thermostat. I
put the old one back on with the same result, no
power. I'm pretty sure I blew the transformer but
can't be sure. Do you have any suggestions on how to
narrow down the problem, and is replacing the
transformer very difficult? I'd like to fix this
myself. Any help at all you could provide would be
greatly appreciated!

labman

Changing the transformer isn't a big deal. First, check to see it was protected with a fuse. Usually they are inline to one of the wires to it, or on the control board for the furnace. You should be able to find a new on at a hardware or home center. Radio Shack also has ones that will work. This time you will be working with 120 volts, so make sure you have the right breaker.

It helps if everything uses the same color code, but most thermostats can be made to work with most systems. Post back with the details.

nynks2351

Prior to pulling out the transformer I checked for a fuse but didn't see one on the board. There's what I think is a relay and a few other devices but nothing that looks like a fuse. It's a very old furnace, is it possible there isn't a fuse?

labman

My old furnace didn't have one either. After replacing a couple of transformers, I added an inline one.