I have a multi-family and the furnace wasn’t working which heats a tenant apartment and my space (tenant’s heat is included). I called a heating contractor which I had used before and they sent someone over. This was their last chance to redeem themselves since the last time I had a problem I wasn’t impressed by their work. Anyway the technician checked out the furnace and told me the wire from the thermostat to the furnace was bad. I also had an electrican scheduled to do work that day so I had him check it out. The electrician told me the thermostat was bad. I replaced the thermostat and the furnace works now.. I am seriously considering sending the heating contractor’s bill back to them with a note stating I shouldn’t have to pay since they were wrong.