Comfortmaker furnace issue: advice on how to proceed?

bill_b · 10-27-2009, 12:52 PM

I am a homeowner having trouble with a Comfortmaker furnace, and I am not trying to repair it myself (so don't worry). But I do need some advice. I've been working with one HVAC repair firm, but they haven't been able to solve the problem.

This is a two-stage Comfortmaker gas furnace. It's in the attic and installed lying on its side. The model number is: NTP6075GFB1. It is not a condensing unit.

The problem only occurs intermittently - sometimes it will work fine for a day or two, and then the problem will continously occur for a half-day or so. Here's what I hear when the problem is occurring:
- I raise the temp on the thermostat and it clicks on.
- The draft fan starts running immediately.
- The blowers never start blowing.
- The draft fan shuts off after about 90 seconds.
- It tries again and repeats that cycle about 5 minutes later.

I've had several technicians from one firm come to my home over the last few weeks trying to solve the problem. First, they were certain it was the igniter. They replaced that, and it didn't solve the problem. Then they said it was the smart valve. Replacing that fixed it for a day or two, and then problem started again. They replaced that smart valve with another new one - worked for a day or two and problem started again. Replaced the igniter - worked for a day or two, then problem started again. They say they are stumped and are waiting for tech support to call them back. They don't think it's the board since the problem is occurring intermittently.

Other info:
I've been up there myself just to collect some info for them. When the draft fan comes on, I don't believe the pilot is igniting, but I'm not certain. I did smell a moderate (but not large) amount of gas when the furnace should have been firing up. After the 90 seconds, the furnace goes into a soft lockout and flashes a 6+1 code. Nothing on the sticker on the door talks about that code. The sticker mentions 6 as the soft lockout code. But the sticker starts with the heartbeat, then proceeds to 2 flashes and 3 flashes which are for low pressure switch stuck open or closed. There is no indication of what 1 flash might mean.

I'm not sure how to proceed. These guys can't figure out what the problem is. They mention the board but don't seem at all certain that that's the problem. I ask what else might be the issue, since we now know it's not the igniter or the smart valve, and they don't have any ideas.

Do I need to work with a different firm? Or does this sound just as unusual to you?

Thanks for any assistance that you can provide. This has been going on for weeks, and it's driving my family and me crazy.

Plumber101 · 10-27-2009, 03:47 PM

Need to clean the flame sensor and check the flue for an obstruction.

I think cleaning the flame sensor just might solve the problem

bill_b · 10-27-2009, 04:19 PM

Thanks. I'll definitely ask about that.

I actually had another technician come by today (also listed on Comfortmaker's site). He asked if when I last replaced my air filter. I told him I regularly replace it and actually that I had recently upgraded to a more expense, better filtration one. He believes that was actually causing the unit to overheat. He thinks I may be fortunate that the only thing damaged by the heat was one of the diaphragms. He thinks the board is OK and will be replacing the diaphragm later this week. So I'll see if that solves the problem.

yuri · 10-27-2009, 05:10 PM

6+1 means it has gone more than 4 trials for ignition and then locksout. Sounds to me like it is getting gas for ignition but not igniting it. If you have too much draft over the pilot burner it may be sucking the gas away and not lighting it. That is a problem with the high efficiency units but I am not sure why a mid would do it. Perhaps my colleagues may know. Been, Houston ???

Get your tech or the gas utility to check the inlet pressure from the house to the gas valve. It may be too low. I had a gas co meter/regulator fail and drop the pressure intermittently. Almost drove me crazy. Finally the damn meter/reg. failed.

bill_b · 10-30-2009, 09:24 AM

I appreciate the responses!

This whole thing is really driving me crazy. The second company from the Comfortmaker site came out yesterday and replaced the diaphragm (which they believed was damaged from overheating due to a higher-quality, higher-density air filter I was using). They were convinced that would solve the problem. The heat was working when they left. But it was warm in the house last night, so the heat didn't run. I tried the heat when I woke up this morning and the same problem occurred - I heard the draft fan kick on and then nothing else.

Re: high-efficiency furnace - this is an 80%, so not sure but I can mention draft to the tech

Some folks have mentioned water... I have asked them check for it. However, i's not a condensing unit. The attic is dry and sealed very well. So I'm not sure where moisture would appear from.

I'll see if I can have someone check the gas pressure. Would that be a whole house issue? We have two zones and are having no problems with the furnace downstairs - just this attic one. Maybe delivering the gas up to the attic is dropping the pressure just enough...

The fact that this continues to be an intermittent problem is what makes it awful. A lot of typical problems seem like they would cause it to fail every time. I'd like to find out the list of issues that could cause this behavior intermittently and then have these techs check each one of them until they figure it out.

Thanks again for any help you can provide!

bill_b · 11-09-2009, 09:29 AM

FYI - looks like replacing the board has solved the problem - thanks for all for the help