Heil NT series horizontal mount - frustrated !!
Hi there, my home has 3 Heil NTG3 / FBF 80% Eff units - two have never had issues, but one I am ready to take a hammer to.. LOL
Here is the scenario - 1> thermostat calls for heat, and unit does not come on , so I open the blower door, activate the interlock 4-5 times and unit comes on works fine until it sits for a while then it does not come on again. I figured it was a sticky relay on the fan / control board.
After about a week of on/off/on now its dead and no amount of interlock on/off will bring it to life.
So I did some troubleshooting - thermostat is good, so is the interlock switch as is the pressure switch and any limit switches I can get to - when I trip the interlock the transformer hums and applies 24V to the control board so I deduced that it was a nearly 100% chance the fan control board was bad.
I ordered a new one, installed it and SSDD - dead. No difference.
For the hell of it I tried the Air Conditioning - worked fine.
The process of firing goes like this:
1> Thermostat calls for heat
2> Fan control board fires the draft induction motor
3> Pressure switch closes, telling Ignitor module to fire ignitor
4> Once ignitor / pilot is lit ignition module opens gas valve
5> Once temp sensor opens, blower starts
Simple stuff. I have worked on far more complex systems than this, unfortunately, the schematics we can find are rudimentary and not very accurate.
I have not replaced the ignition module, but from what I understand it has nothing to do with staring the draft motor.
I short circuited the pressure switch to "fake out" the ignitor into thinking the draft motor was running and still nothing ...
It is possible a limit switch went out - but seems I cannot find them all to test them...
Any ideas ??