Gas and Oil Home Heating Furnaces - Trane gas furnace won't supply warm air (Merged Threads)

I've got a Trane brand gas furnace. A problem has begun cropping up with it more and more regularly. For some reason, if I switch my thermo to heat and set a temp, the fan will kick on, but the furnace apparently doesn't light, and the system just moves around cold air.

I noticed that if I shut down the breaker to the furnace for a bit (5-20 mins), then switched it back on and then tried to get the heater to click on, it would. However, this has tended to not work as much lately.

There's also a related problem that if I do manage to get the furnace to light and provide warm air per the steps above, it eventually still puts out cold air on restart if the furnace cuts off after having reached the preset thermo temp.

I'd like to know if anybody possibly has a cause for this, and the parts needed to repair it. If it is just a part swap or a simple cleaning, I'd like to do it myself.


Per the posting advice...

1. In which area you live and ambient temperatures you usually experience - Texas, currently temps are running 40 at night to 60 or more during the day.

2. House style and construction details - Wood frame house with brick veneer.

3. Make, model and age of equipment related to the problem. The make is a Trane, I don't have the model on hand right now, and the age is probably around 10 years.


4. Fuel type. Natural Gas.


5. Water temperature and pressures of boiler systems. N/A
6. What type of zoning do you have with your boiler system. N/A

7. Thermostat type. Honeywell programmable thermo.

Thanks.

I would guess the gas valve is only working at times. If you have a meter to test with you can watch to see if you are getting 24 volts at the gas valve. If you have the 24v there when it is not lighting than the valve is going bad.

Probably not a DIY though.

HI duder:

Can you tell us about the ignition system? I don't think you have a standing pilot because yuor blower comes on. Usually, on most electronic ignition systems, the blower doesn't start until power is sent to the gas valve, so your problem me might very well be the gas valve. Can you check for 24 volts at the gas valve with a test meter?

I posted once before but was completely off in regard to what I had.

I have a Lennox NG furnace. I don't know what the model or serial numbers are as I can't seem to find them. If it helps, this unit is about two feet tall and about 4-5 feet wide.

When my heat stopped working, my first thought was that it may be the intermittent pilot module (Honeywell S86H), but some advice I got indicated that the problem may be with the gas supply valve. I've since replaced that but no dice.

Next I had a service person come over and without looking at it diagnose it as a dirty burner assembly and quote me a $300 charge to pull it out and JUST clean it. I took the side panels off the furnace, pulled the burner assembly, cleaned it as thoroughly as could be done, then put everything back together and retried it but again, no dice.

Finally, I found some more advice to check the voltage on the intermittent pilot module on the wires going to the gas supply valve. I'm getting no voltage on the wires (although the ignitor/spark plug lights and the spark is clean, straight, and tight). As such, my thought is that if I change out the module, everything should work fine. I'd like to ask anyone in the know if they agree with this assessment - I'm needing to convince myself to buy the replacement part after already having spent $200 on the GSV which appears to not have needed to have been replaced.

Also, in relation to this question, I was wondering if the Honeywell universal replacement modules would be suitable.

IE: http://www.allpartsgrills.com/item336200.ctlg

The part shown on the linked page is $50 to $100 less than an "exact" replacement from other sources, which would make this much easier to swallow.

Any help (and parts sources) is very much appreciated.

Thanks.

:wall: I purchased a new intermittant ignition module per my last post. I was able to get 24v across the PV and MV wires, but nothing from the PV/MV wire. I also noticed that puffs of gas seemed to be coming out of the pilot line/tube in the path of the spark, so there's some progress. The flames, though, were inconsistent. The spark moved around for almost each puff of gas. The puffs/flames weren't consistently shaped. Most were light blue, but occasionally there was some orange color.

Essentially, I seem to be stuck at the point where I should be able to sustain a pilot and then have the burners light, but because my pilot won't light and stay lit, the burners never get supplied. Anyone got any idea as to why the pilot won't light and stay lit?

Thanks.

If you installed the S8610U1003 module, that's the right one. On a call for heat, the pilot valve portion of the gas valve should open and send gas to the pilot burner. You should have 24 volts between PV and MV/PV at the gas valve. if not, back up to the module and check there. Recheck your wiring from the gas valve to the module. If that's ok, remove the pilot burner and clean it: clean both the orifice inside the burner and the air openings on the outside. Take the tubing off and make sure it's clear. Put the pilot burner and tubing back in and try it. If the same thing happens as you described, AND you're sure the pilot burner and tubing are clean AND you have steady 24 volts form PV to MV/PV at the gas valve, then you'll need to see if the inlet screen on the gas valve is clean. Also check the gas pressure before and after the gas valve. You're looking for about 7"wc before the gas vlave and 3.5"wc after the gas valve. If all that is ok, replace the gas valve.