thermostat up/ temp is down

dogmom

Furnace is emitting heat into all ducts. Registers are blowing hot air out. the furnace goes for about 1 or two minutes, shuts off. and then will restart in about a minute. Filter is clean.Thermostat is set at 68 right now the temp in the house is 64. Had coldest night of year last night temp did not drop that low, was at 69, thermostat was at 71.Why is the temp dropping instead of going up? This happened once before when we had strong winds but it did not drop this low....Furnace is 5 years old. Daughter lives downstairs and is freezing.I had the thermostat at 70 plus the last few days before and had no issues.HELP! It is taking forever for the temp to go up, even if I raise the temp on the thermostat to 70!

icesailor

Thermostat Up/ :

A probable cause of this problem could be that the return ducting on your WA system is too small. Or, it is being blocked by something like a rug over a return grill.grate. The furnace depends on cooler, returning air to keep it from melting down. Just like a hydronic boiler does the same. The radiators remove the heat and the cooler water comes back and picks up more heat. So to does the WA furnace. There was a time that WA systems had a supply and return in every room. Now, to keep costs down, there might be one big return somewhere.

From what you describe, the burner/furnace is going off on high temperature limit. The fan still runs, cooling the furnace HX. The fact that it did it before, in the past tells me that the system is probably working as it should, it just isn't delivering the heated air needed into the structure. Have you checked the filters and changed them? If they are dirty, that will cut down the flow. If the filters are dirty and the flow is restricted, and the burner is cycling, you could burn out the HX.

The other possibility is a bad control but normally, that would shut down the gas burner. I think you have a ducting and air flow problem.

Check the outlet air temperature at an air duct. Here is a third world way to do it. Take a kitchen meat thermometer and stick the probe end in the supply grill. Pick one that is as close as possible to the furnace. I can't tell you what it should be but over 120 would be reasonable. Higher is possible. I think that 140 or 150 is the high limit setting to stop the burner. Take the thermometer to the farthest duct and test it there. That will show excessive duct loss.

This is probably more than you wanted to know.