I have an old Heil furnace NUGI125DK02, and it started not working properly. Have a new thermostat and a new gas valve installed in it, changed out the igniter box, cause the old one wasn't opening up the main gas line. Now the pilot comes on and burners flame up for about 10 seconds, then everything shuts off. Then the igniter comes on trying to light the pilot and it doesn't light. It trys again, then the pilot comes on but burners don't. After a few times the burners turn on and stay on until it reaches correct temperature. Sometimes the burners come back on when it gets under temperature, and sometimes it just stays off, until I shut off the electric to the furnace, or turning it off at the thermostat, and then the process starts over again. The unit doesn't have a flame sensor so I don't think that is the problem, unless its somewhere else that I can't see from the front. Any help would be appreciated.

 

There is flame sensor in there some where. Find the igniter model. There will be a terminal labeled "sense". Trace that wire to the flame sensor.

 

From the igniter comes 2 wires, one orange for the igniter, and one white, a ground to the ignition module.

 

Welcome to the forums.

In the service info for your unit there are two ignition modules listed. One is a smart valve module.
What was the part number on the module you replaced ?

 

If it is electronic ignition, which having an ignitor to light the pilot it is, it has to have some type of flame sensor. Every electronic ignition furnace ever made, as far as I know, has a flame sensor of some sort.

 

Thanks...the original module I had for the furnace is S8610u and the replaced used module is S8600H.

 

The old module had a black wire grounded to itself, instead to a flame sensor.

 

Make sure the GND wire is securely connected to the module. Trace this wire to the burner and make sure its connected and clean. Make sure there are no cracks in the wire.

 

The ground is a good connection to the module, and I will double check the connection to the igniter.

 

Cleaned off the igniter and ground also.

 

Ordered another igniter, and will see what happens.

 

Pretty sure it was the igniter, cause I cleaned off the tip and it works now. Just in case I bought a new one, thanks for the help.

 

Thanks for letting us know how you made out.