Hi!

My question has to do with the on/off switch to the whole system. Can
you repair the switch yourself if it is not working, by buying a new
switch and replacing it. Or do I need to have an electrician since it
is a major applicance?

Most of these systems are pretty straightforward in operation. It would help
to know what you have...brand, type, model, etc.

Also, where is this switch? Is it on the thermostat or somewhere else? I've
seen furnaces that had a light switch wired inline on the AC supply in order
to facilitate turning the furnace on or off.

Be sure to be careful! Turn the power, gas and anything else supplying your
furnace off before you work on it. If you don't think you can work on it
safely, call someone to do the work for you.

William