Service Call Issue

[wazlife]

Hey gang,

I was at a service call on a Coleman 93% furnace (Model: G9T1002OUPC13C Serial: WMKM034750). I had most recently been to this home on Wednesday to replace a faulty HSI. Upon return this morning, the burners weren't properly combusting. Only the far left (out of five) burner was igniting - coincidentally, the one with the HSI located in front of it. This particular model has an enclosure around the burner (sealed). I removed the plate and voila, the furnace lit no problem. I cycled the furnace several times and it continuously lit, however, when I would replace the plate, it would only light the far left burner.

I diagnosed that there is likely a blockage in the intake vent. Is this pretty accurate or am I missing something? Normally I handle mostly oil service calls, so I'm a 'bit' fresh to gas service. Thanks for all the help gang!

[Trainerguy]

How old is the furnace? Where is the flame sensor located? If it is in front of the burner furthest from the one that is lighting, then there must be a flame present there to allow the ignition process to continue. I would check the manifold gas pressure for 3.5in w.c. pressure. Usually if a intake vent is blocked the pressure switch would "open" not allowing the ignition process to start. Try leaving the burner cover in place and remove the intake pipe from the furnace. Does it light properly, then it could be partially blocked.
If the furnace is old there might be a heat exchanger problem that is causing this too happen.
Good luck.
Trainerguy

[harshal]

I had same issue at least 2 times.one time I was able to fixed it by replacing the proper Hsi same as old style and washing the burner.the second time couldn't fix it.I checked air intake was clear too.at that time I replaced the burners and ventor motor too but still the problem existed.then CX has to replace the furnace.I think the second time the problem with the heat exchanger,that was 15 yes old york furnace.

[walker]

I've had this happen a few times, once it was the intake, after i removed it, all burners would fire up no problem.  Another time it was vent motor that wasnt working properly.