Heil Furnace Question

I have an older Heil model NUGI075DF03. It just started this. It lights normally and the fan starts and it heats for about 90 seconds then the burners and pilot turn off for 40 seconds then the process starts all over again and repeats itself until the demand for heat is satisified. The fan doesnt shut off during during this whole process. Thanks for your help

 

It sounds like the burner is cycling on high heat limit. That is usually cause by a dirty air filter, blocked air returns, too many registers closed or the blower not maintaining correct speed.

Start with the first three on the list.

 

What senses the heat temp and where would the sensor be located

 

If I've located the correct information.... you have a combination fan thermostat/high heat limit control. It should be a metal box just above the burners. It's rectangular, about 1-1/2"W x 3"H.

In the link below it's 26A in the diagram.


Sears parts direct/Icp-Parts/Model-NUGI075DF03

 

Your post got me thinking. I changed my furnace filter about 2 weeks ago. I didnt think to check that, when I opened up the blower door I found the air filter all bound up and must have been restricting the airflow. I put in a new one and now it seems to work ok. Thanks so much for your help

 

The last few days once in awhile it will still cycle the burners off about 6-7 minutes into a cycle. My question is when I watch the dial on the fan and high heat thermostat it seems to be jerky in its operation. Do these cause problems? I also installed a more expensive air filter made to filter more than a fiberglass one can this restrict airflow enough to cause problems? If I pull the filter out an inch or so the temp never hits the high limit so it seems like not enough airflow going through. All of my cold air returns are ok and unobstructed. Let me know your thoughts

 

Those controls do move jerky. That's normal.

Some filters are more restrictive than others. Some people have found that the less expensive filters work better.

You said your cold air returns are ok and that's good.
How about the supply registers. Too many closed down registers can also cause a flow problem.

 

Yesterday I got a cheap fiberglass filter and put it in and now it does the opposite the burner stays on and the fan cycles off due to low heat. The one I purchased is really cheap and doesnt seem to be much better than not having a filter in at all, so, I think I need to find a happy medium with filters. What temp should the air be when it is coming out of the registers on the first floor. I tested mine this morning and it was right around 109.00? I also checked and all of our registers are open Thanks for your help!!