Help! New to gas and having serious problem. Tried replacing Honeywell digital thermostat batteries, tried reprogramming all temps multiple times. Turned off thermostat, gas keepis running temp at 80 degrees. Finally out of deperation and perspiration, I had shut off the furnace switch. I must leave for work now and I am not looking to waste more costly fuel in having summertime temps in my NY home. Can anyone help? The gas furnace is a HydroTherm HC-125C, not sure how old.