Forced air propane heat system, odd "issue".

brad1138

Recently I have noticed when the heat comes on, sometimes it comes on for about 1-2 seconds, then it goes right back off. About 5-10 seconds later, it comes on again normally as it always has, and works fine.

I think it is only happening when it comes on via scheduled timer (I use Nest thermostat), but I am not sure. I have noticed it less than a half dozen times over the last couple months. If that is the case, I would think it is likely a glitch in the thermostat.

The house is an 2006 and it is the original furnace.

Any thoughts?

Thanks

EdTheHeaterMan

When was the last time your furnace had routine maintenance?

In order to eliminate the thermostat as part of the issue, place a standard thermostat on the wall and see if the problem goes away.

pecmsg

https://forum.heatinghelp.com/discussion/comment/1822582#Comment_1822582

an issue with a NEST

Impossible!

EBEBRATT-Ed

How many wires are hooked up to the Nest? It needs 3 wires to work properly. If it only has 2 wires the internal battery will probably not charge.

brad1138

https://forum.heatinghelp.com/discussion/comment/1822588#Comment_1822588

brad1138

https://forum.heatinghelp.com/discussion/comment/1822582#Comment_1822582

Ummmm, when it was installed... :)

I don't have a standard thermostat laying around.

If it is only happening when it comes on as part of the daily schedule, I would think it has to be the Nest.

EdTheHeaterMan

That version of the NEST looks like the one I had on my home. The LP heater you have… Is if a furnace with ductwork and registers that blow hot air? if yes, does it also have air conditioning?

OR

Is your LP heater a boiler that has pipes that carry hot water to radiators or baseboards that heat up the rooms?

I dont disagree that it could be the thermostat, I just like to know it is the thermostat before I try to fix the thermostat.

Read what I used to say to the mechanics the used to work for me: "After you make that expensive repair and you still have the same problem, What will you check next?"

brad1138

https://forum.heatinghelp.com/discussion/comment/1822665#Comment_1822665

It says model 3.4.

Forced air with ductwork and registers that blows hot air. Does not have AC.

EdTheHeaterMan

OK. There is always the possibility that the flame sensor may need to be cleaned or replaced. Another reason for that short on/off then back on could be a bad ground connection from the flame sensor control the the flame sensor location at the burner.

In most new furnaces the flame sensor is either the spark ignitor rod, or a separate flame rod the sticking into the gas flame. A small electrical current is sent by the ignition control to that rod. The flame conducts electricity from the rod to the burner. Then the signal then returns to the ignition control by way of the metal burner that is attached to the frame of the heater with metal screws, and eventually back to the control with a ground wire from the heater cabinet to the control. It is important to have a good ground circuit with no corrosion to add resistance to the signal. Regular maintenance should include cleaning the flame sensor and tightening the screws that mount the burner to the cabinet along with changing air filters, measuring the gas pressure, and cleaning dirt out of the burner jets.

Cleaning and maintenance is usually less expensive that replacing a thermostat or other parts.

JOutterbridge

Nearly 20 year old propane furnace? My guess would be flame sensor needs cleaning or failing ignitor not getting hot enough on first try anymore. If you have corrosion, sometimes the burners need cleaning as well to complete the flame sensor circuit. I'd try the sensor first though, easy 20 minute fix for most.