Furnace shuts off - won't restart without reset

Bob_4

First, we do operate a CO detector.

From time to time our furnace will no longer turn on and the house will cool off until we "kick-start" it by turning the thermostat off then on. We can go weeks, days or just hours between "fits". Past couple days it is constantly stopping.

We first noticed the problem last winter right after the overheat sensor failed. It was replaced with a slightly cooler switch (220F). The furnace guy said it would work the same. I don't know if there is any connection.

The furnace is a Concord 90% Efficient, gas fired, forced hot air unit with a White-Rodgers mercury switch thermostat, 5 years old. When the system is working, the thermostat does keep the house properly conditioned. Moving the temp control makes no difference, ONLY toggling the on/off switch on the thermostat will kick on the furnace. This fix always works.

I replaced the thermostat with the "round" Honeywell programmable without any improvement. The gas company replaced the furnace circuit board, also without improvement.

The tech said the overheat sensor is working properly. The main fan and the exaust fan both appear to work whenever they are told to.

Any ideas?

Pat_2

Next thing to check would be the flame sensor. Over time they get dirty and then will drop out the burner erratically and the furnace will have to be manually reset. If you know how to test and have the right test equipment, that should be done first. If you want to clean it and see if it improves, clean with fine steel wool and don't touch the sensor with your fingers after cleaning. If it is pitted or scorched badly I would replace it.

Hope this helps

Pat
Bell Plumbing & Heating

mike terry

furnace

get a service tech on the job ....take a heat rise across the furnace....check for resricted filter is there an a/c coil on this furnace? check firing rate. over a period of time dust builds up on the vanes of the blower wheel reducing air flow and raising furnace discharge temp.insulation that has come loose could restrict air flow and cause overheating. some condensing gas furnaces have close spaced fins that can get clogged and over heat a furnace.

Bob_4

I do have the gas company looking at it (and THEY can't seem to figure it out). I scared of gas. The t-stat was about as far as I would go with a furnace.

The filter *was* a monster 6" thick unit. It clogged and allegedly caused the overheat to fail. I was unable to find a replacement (still looking for a reasonable replacement). The tech told me the filter maker was out of business? The filter is currently out. The cold returns are all wide open.

Is the flame sensor the same item as the over-heat sensor?

Pat_2

The Flame Sensor is a different component than the limit (over heat switch). It is in the burner and actually senses whether the burner ignited or not. Will shut down the system if it does not sense an actual flame. Ask the tech from the gas company if he checked this specifically. If not, I would suggest contacting an independent heating company to check the unit. Ask if they use a checklist when inspecting a heating unit. Those company's that don't usually miss things like this over and over.

Pat / Bell Plumbing & Heating