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Drider75 12-30-2012 04:10 PM

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 ??


Tator1076 12-30-2012 04:32 PM

Were is the draft motor getting its power? Is it the board or do u have smart valve?

Drider75 12-30-2012 04:41 PM

Draft motor getting its power direct from the fan board. Dwg attached. This is a pretty simple system, if I had the schematic for the main board I am sure I could figure it out straightaway, or at the very least troubleshoot it down to the fault - but alas - I'm good at finding stuff but cannot seem to locate it anywhere.

Gas valve is an intermittent pilot dual automatic type, not a smart valve.

Drider75 12-30-2012 04:42 PM

System diagram...
1 Attachment(s)

Drider75 12-30-2012 04:47 PM

CCA Part # / Model #
1 Attachment(s)

Tator1076 12-30-2012 04:49 PM

Check that 6 way plug. sometimes that can come undone and cause problems

Drider75 12-30-2012 04:52 PM


Originally Posted by Tator1076 (Post 1082687)
Check that 6 way plug. sometimes that can come undone and cause problems

It was on/off several times when I changed out the control board - doubt its that...

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