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jlsjoe

join:2010-11-24
New Ulm, MN

gas furnace problem

Hello all,

I have a 13 year old Lennox gas furnace. When I started it this year it started fine. After one cycle it shut off as it should but the main blower fan continued to run. When the temperature dropped to where it should have kicked in again the main fan continued to run and the furnace did not start again. I shut off all power and tried again but as soon as I power up the unit the main blower fan kicks in immediatly and the LED is dark on the control board. Blower fan kick in but that is is.

I should mention that by main blower I'm reffering to the heat circulation fan, not the draft inducer. I'm thinking it may be a connection problem as I am no longer getting any light from the led on the control board. Circulation fan still comes on as soon as I power it up but that is the only thing that happens.

Any ideas?

Thanks,

Joe



Msradell
P.E.
Premium
join:2008-12-25
Louisville, KY

What type and model is your furnace? It will make a big difference if it is a low efficiency or high efficiency furnace with or without a pilot light.

My first guess wouldn't be a connection. I would more likely lean towards the control circuit problem. Possibly in the heat defective circuit, if it thought the firebox was still hot it would run the fan to cool it and would not allow the furnace to fire again until a certain lower temperature was reached.



jack b
Gone Fishing
Premium,MVM
join:2000-09-08
Cape Cod
kudos:1
reply to jlsjoe

A lot of integrated circuit boards will run the main blower for up to a minute on power-up. Check the 3 amp fuse on the board.
--
~Help Find a Cure for Cancer~
~Proud Member of Team Discovery ~


jlsjoe

join:2010-11-24
New Ulm, MN
reply to Msradell

it is a Lennox m/n G26Q3-75-1, High efficiency rated at 92% efficiency No standing pilot light. Defective heat circuit makes sense. It seems that it will run the main blower much more than a minute. I'll let it run and see what happens and check the fuse also. Any ideas why the LED seemed to quit working just as this problem occured? It was working the first time I started the furnace. Now it does not flash a code or anything, just stays off.

Thanks



Jack_in_VA
Premium
join:2007-11-26
North, VA
kudos:1
Reviews:
·Millenicom

Not that up to speed on the newer furnaces but I remember I had a hot water baseboard boiler that had several high temperature cut outs. One on the hot water to the baseboard heaters and one on the stack before it connected to the chimney. Both of these were manual reset and cut the power to the controls.



Pacrat
Old and Cranky
Premium,MVM
join:2001-03-10
Cortland, OH
kudos:2
Reviews:
·Time Warner Cable
reply to jlsjoe

We woke up this morning to about 58 degrees in the house and no heat coming from our 5-year old Carrier gas furnace. After a very courteous, timely, and helpful visit from our local HVAC serviceman, it ended up being a lightly oxidized flame sensor that needed attention. Seems it refused to allow gas to be delivered to the combustion chamber when there was no flame to use it. A few quick wipes with what appeared to be fine crocus cloth and all was good. While he was here, he also performed some routine maintenance that was probably overdue. What amazed me, moreover, was that he was able to get into the thermostat to read the trouble codes for all the "incidents" since the furnace was installed. I didn't know the codes were stored there, or could be retrieved like that. I knew you could count the LED flashes to get a current trouble code, but I never knew a history was available.

Not to hijack your thread, but could you be experiencing the same problem? My fan was continuing to run also.
--
Alcohol kills germs! Stay drunk... Stay healthy!



SandShark
Long may you run
Premium,MVM
join:2000-05-23
Santa Fe, TX
kudos:3
reply to jlsjoe

Usually when a furnace has tripped out on a high temperature limit, the control board will lock out the furnace and the blower will run continuously.

If you are not comfortable servicing your gas furnace, I suggest you contact your local Lennox technician for any repairs or issues that are outside your comfort zone. Property damage, personal injury and death can occur from improperly repaired or maintained gas furnaces. Replacing a part doesn't always resolve the issue that caused the part to fail!


jlsjoe

join:2010-11-24
New Ulm, MN

Good point.



Jack_in_VA
Premium
join:2007-11-26
North, VA
kudos:1
Reviews:
·Millenicom
reply to SandShark

said by SandShark:

Usually when a furnace has tripped out on a high temperature limit, the control board will lock out the furnace and the blower will run continuously.

If you are not comfortable servicing your gas furnace, I suggest you contact your local Lennox technician for any repairs or issues that are outside your comfort zone. Property damage, personal injury and death can occur from improperly repaired or maintained gas furnaces. Replacing a part doesn't always resolve the issue that caused the part to fail!

Excellent post and very good advice.

TheMG
Premium
join:2007-09-04
Canada
kudos:3
Reviews:
·NorthWest Tel
reply to SandShark

said by SandShark:

Usually when a furnace has tripped out on a high temperature limit, the control board will lock out the furnace and the blower will run continuously.

Although the LED on the control board should then be blinking in a certain pattern indicating the fault, shouldn't it?

The fact that the LED does not come on but the blower motor relay remains energized (an indication that the board is in fact receiving power) leads me to believe the board is most likely FUBAR.

Then again some furnaces and control boards are of peculiar design, so it is advisable to check all the other possibilities before replacing anything. A multimeter/voltmeter is a great troubleshooting tool in this situation, allowing you to determine the state of all sensors, switches, limits, and power sources. Furnace wiring diagram also very helpful.

Good advice not to blindly replace parts.


Msradell
P.E.
Premium
join:2008-12-25
Louisville, KY
reply to SandShark

said by SandShark:

Usually when a furnace has tripped out on a high temperature limit, the control board will lock out the furnace and the blower will run continuously.


This certainly sounds like the most likely cause of the problem.

jlsjoe

join:2010-11-24
New Ulm, MN
reply to TheMG

The non functioning LED is what really has me confused.



SandShark
Long may you run
Premium,MVM
join:2000-05-23
Santa Fe, TX
kudos:3

said by jlsjoe:

The non functioning LED is what really has me confused.

I missed that part in your earlier post. This is a problem. You're sure you put your eye close to the site glass. With some furnaces/boards, the LED doesn't align directly with the site glass.

To your knowledge, is the board the original board? I know for a fact that the original boards have been replaced with a newer replacement kit.

Is the blower still running? If not, you're sure the blower door is in place and the door switch is engaged?

jlsjoe

join:2010-11-24
New Ulm, MN
reply to TheMG

The non functioning LED is what really has me confused.


jlsjoe

join:2010-11-24
New Ulm, MN
reply to SandShark

This particular unit has two access doors, an upper and a lower. I have a direct view of the LED with the top door removed and can say definevitly sp? that the LED is not lighting/flashing at all. The first time I started it was with this door off and it worked fine and the LED was functioning. To be sure I replaced the upper door and tried again and got the same result. I do know for a fact that the original board has not been replaced as I bought the furnace and have never had to have any work done on it before. The main heat circulation fan starts and continues to run as long as there is power to the unit but nothing else happens. The first time I started it this year on powering it up the LED flashed, the draft inducer fan kicked in then the pilot lit then the main burner lit. About 10 seconds later the main blower kicked in and it went through one heating cycle just fine. When the fire went out the main blower continued to run until powered the I furnace down about 1 hour later when I noticed that cold air was blowing through the ducts. I did leave it run for about 30 minutes earlier and it continued to run. Blower door is in place and the switch is engaged.



The Pig
I know you want to be me
Premium
join:2009-09-11
reply to jlsjoe

Is the furnace lighting up? if it is not lighting up the fan will not stop blowing!
If not it could be a carbon build-up problem or something in your flue.



SandShark
Long may you run
Premium,MVM
join:2000-05-23
Santa Fe, TX
kudos:3

1 recommendation

reply to jlsjoe

According to what I can find online, that furnace came with a SureLight integrated control board, which has two LED lights, not one. It should say "SureLight" on the board. The LEDs should be located at the bottom right-hand side of the board just above the low voltage terminal block.

If this is the case, kill power to the furnace. Remove the blower access door. There may be a control box cover for the control board. Remove that cover. Set the thermostat to a call for heat. Supply power to the furnace. Engage the door interlock switch. Then, come back and report what you have observed.



jack b
Gone Fishing
Premium,MVM
join:2000-09-08
Cape Cod
kudos:1
reply to jlsjoe

It's possible a rollout (spill) switch opened, or some other safety/limit that needs resetting/replacing after figuring out why it opened.
--
~Help Find a Cure for Cancer~
~Proud Member of Team Discovery ~



zen1

@optonline.net
reply to jlsjoe

guys, here's the service manual. there's a circuit breaker on the control box that may be tripped if the LED's never come on!. or a bad board.. »www.cozyparts.com/Lennox-Parts/f···2004.pdf



SandShark
Long may you run
Premium,MVM
join:2000-05-23
Santa Fe, TX
kudos:3

The circuit breaker is for the transformer. If the breaker tripped, neither the blower or anything else would operate. You are right that the board being bad is one possibility. However, before we condemn a board, we need to eliminate all other possibilities first. That's why I asked the OP to perform the tasks in my previous post.



zen1

@optonline.net

said by SandShark:

The circuit breaker is for the transformer. If the breaker tripped, neither the blower or anything else would operate. You are right that the board being bad is one possibility. However, before we condemn a board, we need to eliminate all other possibilities first. That's why I asked the OP to perform the tasks in my previous post.

looking at the fault codes, at least one LED should be doing something, both staying out are not on the chart. it's possible the fan relay froze closed, which can happen, which could explain the fan staying on, and the board is not getting power though. we'll see when the OP responds.

jlsjoe

join:2010-11-24
New Ulm, MN
reply to SandShark

My unit has a box mounted behind the upper access cover above the draft inducer fan. There is one LED near the top approx. center of the box. It is among the other conections on this box. The code listed for no LED says no power or fault exsists. The name plate on this box is Johnson coontrols, no mention of "Surelight". There is a Lennox board mounted behind the lower access door but there are no LEDs present.
I went through the procedure suggested by SandShark with the same results. After I set the thermostat to call for heat, supply power to furnace and engage the door interlock switch the main blower kicks in with no other results. LED does not light and draft fan does not engage.



SandShark
Long may you run
Premium,MVM
join:2000-05-23
Santa Fe, TX
kudos:3

1 edit

Okay, I failed to realize you have a G26 -1 model. The SureLight boards are installed on -3 through -6 models. So, according to the unit information literature (page 16), if there is no LED light present on the Johnson Controls Ignition Control Module (assuming there is voltage to the unit) the module is, as you noted, defective and needs replacing.







Edit - Added attachments

jlsjoe

join:2010-11-24
New Ulm, MN

I just finished replacing the old johnson controller with a new honeywell unit and my problem is still exactly as it was before. I'm thinking there is power or the main circulation fan would not operate. All is just as it was with the old board.


jlsjoe

join:2010-11-24
New Ulm, MN

I pressed the limit switch mounted on the side of the combustion chamber, it did not appear to be out, now it is working! I will see how it acts when it cycles to a new heating cycle. I think I may have wasted some money and you peoples time. Very sorry, will report further findings.

Joe


zen1

join:2010-12-06

said by jlsjoe:

I pressed the limit switch mounted on the side of the combustion chamber, it did not appear to be out, now it is working! I will see how it acts when it cycles to a new heating cycle. I think I may have wasted some money and you peoples time. Very sorry, will report further findings.

Joe

that's odd, if there's no power to the board, the blower shouldn't be coming on!. and if there IS power to the board, there should be an LED coming on to indicate a fault!. that limit switch must be wired funky!. anyway, glad it's working, and you really didn't waste money, the money you spent could have gone to a tech for working on the furnace!. anyway, if that problem happens again, it may be that funky wired limit switch needs replacing.(assuming it's not truly overheating). you'd think that would be auto reset not manual reset!.