lennox gas furnice will fire sometimes

Problems related to residential installations.

lennox gas furnice will fire sometimes

Postby ncwetbar » Mon Jan 28, 2013 2:26 pm

hey I have a Lennox furnace, Im having problems with. I was getting blinking error codes for limit switches. So I shorted all of then out and used a temp probe to make sure I didnt over heat it. It did get up to about 150 and shut off again with a error code of -"Improper main ground or line voltage below 75 volts; - Broken ignitor; - ignitor circuit."
I checked the voltage and the ground. I'm not sure about the broken ignitor because it did ignite for 45 sec.

So I think I have two - #1 it is over heating, I checked the fan and filters all seemed OK and the coil is clean. I'm not sure what else can cause over heating.
I tried to check the gas pressure but the screw is stripped out and I could not remove it.

problem # 2 I am just lost, any clues?
ncwetbar
New Contributor
 
Posts: 5
Joined: Mon Jan 28, 2013 2:18 pm

- lennox gas furnice will fire sometimes

Postby Freon » Mon Jan 28, 2013 3:54 pm

How old is the furnace. Did it work perfectly until this recent set of problems. Any new construction or changes to the furnace.

The voltage and ground error may be due to a loose connection. Turn off the furnace at the main breaker box and check all 120 volt connections including the switch at the furnace. Check the hot (black), neutral (white) and ground (bare copper) for any signs of a loose connection. Check the connections at the furnace control board. If you're comfortable with electricity, I'd check the connections at the main breaker box making sure the neutral and ground wires are bonded securely.

Now turn on the power BUT do not call for heat. See if you get the improper main ground error now.

If the board shows no errors set the thermostat to 5 degrees above the house temp. Now go to the furnace and watch it run. You want to see if the burners shut off while the main blower keeps running. Then you want to see if the burners restart or if you get the high limit error. If the burners shut off then you know you have either an overheating heat exchanger or a faulty high limit switch. If you check the furnace installation manual you will read about the expected temperature rise through the heat exchanger. It's usually around 60 degrees. So if you measure the air temperature as it immediately leaves the furnace and subtract the house air temperature (air temp into the furnace), you want a number less than 60 (or whatever your manufacturer says).

If you determine you do not have inadequate air flow through the heat exchanger (temp rise is too big) you'll need to look at the duct system and especially the returns to see all are adequately sized. Another possible option is change the blower speed but you need to know your duct system can handle increased air flow, which I doubt.
Freon
Most Valued Contributor
 
Posts: 735
Joined: Sat Jun 18, 2011 11:26 am

- lennox gas furnice will fire sometimes

Postby ncwetbar » Mon Jan 28, 2013 11:43 pm

The problem it is even kicking out before the 45 sec warmup before the blower comes on. Im thinking flame problem look at the flame, and let me know what you think?


how does this flame look to everyone?

*.*/watch?*&*

It is 20 years old, but looks well taken care of. Was working fine till Saturday.


edit-ok it will not let me do that, hum, that sucks.
ncwetbar
New Contributor
 
Posts: 5
Joined: Mon Jan 28, 2013 2:18 pm

- lennox gas furnice will fire sometimes

Postby Freon » Tue Jan 29, 2013 12:35 pm

I assume there is not an inducer blower that starts in the very beginning of a heating cycle to get the proper air flow. Therefore if you're losing burner flame after 30 to 45 seconds I would check the flame sensor. It should be a thin metal rod with a porcelain base and one wire attached. Make sure that metal rod (maybe 2" long) is well positioned in the flame. And you might try gently rubbing any rust off of it with emery cloth.

Do I understand you when you said that with the all the safety switches jumped, the furnace ran as you would expect? If that is true then it may not be a flame sensor issue. Please let me know how the furnace behaved with all safety switches jumped.

To post a url, do the following form... w .w .w. myurl . c o m slash files slash pictures slash mypicture.jpg
Freon
Most Valued Contributor
 
Posts: 735
Joined: Sat Jun 18, 2011 11:26 am

- lennox gas furnice will fire sometimes

Postby ncwetbar » Tue Jan 29, 2013 10:19 pm

yes the inducer fan comes on and is proved and the burners fire. I got the plug off and checked the pressure it was 3.2. I brought it up to 3.5 and of course it does the same thing. It pops the limit switch just before the fan starts, but then after the fan run it will refire and run for 45 min or so and then give the low voltage error code. This time I ran it with the furnace doors open to make sure there was not a air problem. Im at a lost! the only thing I can think of is the board. Any thing else I should try. oh yeah I did check the exhaust and it was 148 just after the fan but went down quick as I checked further up the stack, so it is not blocked
ncwetbar
New Contributor
 
Posts: 5
Joined: Mon Jan 28, 2013 2:18 pm

- lennox gas furnice will fire sometimes

Postby Freon » Wed Jan 30, 2013 12:08 pm

New test. At the thermostat, set the Fan to ON, not Auto. Now call for heat and go observe the furnace burners. Do they now run constantly until the thermostat set temperature is reached or do they cycle like before. Do you get the low voltage error.

If the burners run constantly until the thermostat set temperature is satisfied and do not cycle, then the high limit switch and air flow through the heat exchanger seem to be good.

If you get the low voltage error, does it happen after the heating cycle is fully completed and the thermostat set temperature is satisfied or does the low voltage error happen with the burners shutting off before the thermostat set temperature is reached.
Freon
Most Valued Contributor
 
Posts: 735
Joined: Sat Jun 18, 2011 11:26 am

- lennox gas furnice will fire sometimes

Postby ncwetbar » Fri Feb 01, 2013 2:52 pm

If the fan starts first it will run for 30 or 45 min or so and give the ground error. The exchanger has to be blocked, how can I get down in there
to check/clean without a camera?
ncwetbar
New Contributor
 
Posts: 5
Joined: Mon Jan 28, 2013 2:18 pm

- lennox gas furnice will fire sometimes

Postby ncwetbar » Fri Feb 01, 2013 2:54 pm

If the fan starts first it will run for 30 or 45 min or so and give the ground error. The exchanger has to be blocked, how can I get down in there
to check or clean without a camera.
ncwetbar
New Contributor
 
Posts: 5
Joined: Mon Jan 28, 2013 2:18 pm

- lennox gas furnice will fire sometimes

Postby Freon » Fri Feb 01, 2013 4:56 pm

(Q) is a a question mark.

If the heat exchanger were blocked the burners would cycle with the main fan (blower) on. As I asked, did you observe the burners when you did the test with the Fan set to ON at the thermostat (Q). If the burners ran constantly until the voltage error then the heat exchanger is not clogged. However if the burners cycled on and off while the furnace ran for 30 to 45 min then you may have an air flow problem and one source could be the heat exchanger. Do the burners cycle on and off during this 30 to 45 minute run (Q).

The real troubling issue is this low voltage error. When you get the low voltage error, has the thermostat set temperature been satisfied and the furnace is shutting down because there is no longer a call for heat (Q). Have you had any electrical work done at your house(Q).
Freon
Most Valued Contributor
 
Posts: 735
Joined: Sat Jun 18, 2011 11:26 am


Return to Residential