I just turned on the heat for the first time and my furnace won't light

Questioner: Steve
Category: Heating, Air Conditioning, Fridge, HVAC
Private: No

Subject: ignition problem - Goodman GMNT100-4 furnace
Question: QUESTION: Hi Mike - I stumbled across this site while trouble shooting my Goodman GMNT100-4 furnace and thought I would give it a try. This is a used furnace that I had installed in my workshop (professional install) - it has been in place for almost 2 years without any issue. It is also fueled by Propane.

When the thermostat trips, it turns on the furnace as normal . The blower motor kicks in (draft motor?). The ignitor begins to glow a short time after this, and then the gas valve supplies gas. This is where things start to go wrong. There are 5 "burners" / tubes. The first one with the ignitor begins to burn the propane, but the other 4 tubes never begin to burn.

I pulled the front cover so I could watch the circuit board and after it cycles a few times, it shuts down and the indicator light blinks once indicating failed ignition (yeap, it failed to ignite properly). Listed problems include gas pressure and ignitor. The ignitor is new.

I did check the obvious and the propane tank (500 gallon) is 40 percent full. I did not check pressure post regulator as I have no easy way to do that currently.

Am I looking at a propane regulator problem or is it possible it is the gas valve itself? Any other thoughts?

This problem started gradually and now it will not ignite fully at all.

Ideas?

ANSWER: Your igniter is definitely not bad as it is getting hot. So move to the next problem you are not getting complete ignition, the possible causes are obviously improper fuel pressure ( you need to be able to check this to properly diagnose), Restricted fuel delivery (plugged orifices, screens or strainers), too much or too little combustion air (bad heat exchanger). So where do we go from here, first because you do not have any pressure diagnostic equipment you can theorize about fuel pressure but without knowing that is just a rabbit hole and has to be saved for last. So that leaves you with restriction or improper combustion air. We need to recognize that we are talking about issues of safety first so with resriction you can easily take off all the burner orifices and get a torch cleaning kit or fine wire and make sure everything is clear then move to combustion air. Because your system is not shutting down on your draft motor or pressure switch it is not likely that you have a bad fan or blockage so that leads me to a possible bad heat exchanger. Make sure your indoor fan is not running while the furnace is trying to light. If it is not then cobustion air is probably not an issue. If it is and when you make sure the fan is shut off the furnace lights ok then that is a red flag for heat exchanger issues and you need to get a new furnace. If none of this advice works you need to get proper pressure testing equipment and make sure your fuel pressure matches the design parameters on the information plate of your furnace. I know that is a lot of information but that is just some of the things you have to consider when you are working on this equipment.