Question about Heating & Cooling

5 Answers

High limit switch open on armstrong furnace

I have an Armstrong Air furnace that is not blowing hot air. Noticed the LED light is flashing four times, which, according to the alarm code means I have a high limit switch open. Turned the furnace off and back on but that didn't do any good. How do I find and manually close/reset the high limit switch??? Thanks!

Posted by on

  • 5 more comments 
  • Anonymous Oct 21, 2008


  • Anonymous Dec 14, 2008

    new 90plus eff. goodman furnace......4-flashes h-l-o, there seems to be 2 or 3- limits,which one is problem,,,ok to bypass?

  • bradlytdot Dec 19, 2008


  • Anonymous Dec 23, 2008

    it's supposed to be as simple as a reset button--how do you do it on a york diamond 80

  • A_Artanis Dec 26, 2008

    Same thing - no hot air, LED flashes 4 times. Where is the stupid switch, what does it look like? I have Ultra V, Tech 80 model of Armstrong Air. It's Boxing Day, everything is closed (of course!), it's -30 outside.


  • John Ferrell
    John Ferrell Jan 18, 2017

    Hey, I love your question that asks how to manually reset the high limit switch. I'm sorry to hear that turning the furnace off and on didn't work. Recently, I have noticed that my furnace hasn't been acting up. I think that hiring a professional might be a good choice when looking for the solution.

  •  John
    John Jan 18, 2017

    An "open" on a high limit switch could possibly means it's defective and needs to be replaced. Or you may have a clogged filter or some sort of defect or obstruction in the blower's squirrel cage that's triggering the high limit switch to "open". A furnace is at risk from overheating anytime the air flow is restricted; so When the high limit switch "trips", the heating element will shut-off but the blower will continue to run to cool off the heat exchanger. If you have no experience with troubleshooting and repairing HVAC system, hire a heating specialist. Remember, the high limit switch is a safety device- don't mess with it if you don't know what you're doing!



5 Answers

  • Level 1:

    An expert who has achieved level 1.


    An expert that has over 10 points.


    An expert whose answer got voted for 2 times.

    Problem Solver:

    An expert who has answered 5 questions.

  • Contributor
  • 5 Answers

If you know where the high limit switch is you can always cut the two wires and wire them together causing the limit to close. But what you have to watch out for is why the high limit is not closing. That means in your return air either you have a dirty return air duct, dirty filter, or you don't have all your registors open to allow the heat to escape the heat exchanger. Just watch over riding the system. The high limit switch should either be on or behind the blower, in the middle of the system right under the heat exchanger. any other questions about hvac just ask.


Posted on Jan 17, 2009

  • Level 2:

    An expert who has achieved level 2 by getting 100 points


    An expert that got 5 achievements.


    An expert who has answered 200 questions.


    An expert whose answer got voted for 20 times.

  • Expert
  • 210 Answers

You need an ohmmeter. Start checking all thermal limit switches
and fuses. Remove one wire when checking and also turn voltage off to unit. It could be a resetable switch, start pressing all the pop up buttons on the switches.
The cause could be simply - dirty air filter or a blower assy problem, or dirty flue vent, or induce draft fan problem.

Posted on Mar 23, 2008

  • Level 1:

    An expert who has achieved level 1.

    New Friend:

    An expert that has 1 follower.


    An expert whose answer got voted for 2 times.

  • Contributor
  • 1 Answer

I have an Armstrong high efficiency 90+ Condensing Gas Furnace. The Blower works on Cool, but not when the Heat is on. The LED flashes 3 times: Fault is Pressure Switch open with inducer on"

Where is the combustion blower? Is this an easy fix?


Posted on May 12, 2010

  • Level 1:

    An expert who has achieved level 1.

    New Friend:

    An expert that has 1 follower.


    An expert whose answer got voted for 2 times.

  • Contributor
  • 1 Answer

The limit switch is one of several built-in safeties designed to protect the furnace and prevent a possible explosion. Rule # 1, i.e. don't put jumpers or do any other things that you don't fully understand as it is extremely dangerous to play with furnaces. Remember, you are not a certified HVAC mechanic. Rule # 2, i.e. read the manual and follow simple steps such as find any blockages, open closed registers, etc. Rule # 3, i.e. if all the above doesn't help, don't be a frigging idiot and call a professional !!!!!

Posted on Dec 29, 2009

  • Level 1:

    An expert who has achieved level 1.

    New Friend:

    An expert that has 1 follower.

  • Contributor
  • 1 Answer

I had the same problem. The furnace was cold but it get 4 blink failure code right after the fans were on. I traced the Orange cable that come out of the High Limit switch to the connector to the control board. When I push the cable from side to side right at the connector, I heard relay clicking and the 4 blink failure code was gone. I put two toothpick and jam and push the cable to one side and the furnace fired up. I will fix it later. At lease I found the problem as simple as with the table connector.

Posted on Nov 25, 2017

1 Suggested Answer


6ya staff

  • 2 Answers


Hi there,
Save hours of searching online or wasting money on unnecessary repairs by talking to a 6YA Expert who can help you resolve this issue over the phone in a minute or two.

Best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.

Here's a link to this great service

Good luck!

Posted on Jan 02, 2017

Add Your Answer

Uploading: 0%


Complete. Click "Add" to insert your video. Add



Related Questions:

1 Answer


Does the furnace stays off?.
Furnace are ment to cycle on and off because of limits .If you set to 70 furnace would cycle several times before reaching that temperature.
Just make sure your filters are clean and you got proper return air flow because lack of air flow will cause furnace to shut off sooner than normal

Jun 08, 2017 | Heating & Cooling

1 Answer

Armstrong GUK125D20-2B won't ignite

Did he check the Pressure switch was it filled whit water can you make the switch open on the pressure switch when blowing on it? Is the hose from the inducer motor opened and not blocked ? also if there is a block after the inducer motor it will not Ignite. If the Tech does not know how to check a pressure switch get a new tech.

Oct 06, 2012 | Honeywell Furnace Air Pressure Switch...

1 Answer

Intertherm mmha070

Hi, did he bypass the high limit to see if it was bad? Sounds like you are getting false codes and you have a problem in your module or main board, which ever you have. The way it is acting, saying the high limit is open but the tech says its not, I would change the board.

Nov 14, 2011 | Intertherm P3RA-048K Air Conditioner

1 Answer

I have 1990 Armstrong gas furnace Ultra III 80, Model EG6G75dc8-4 .\r\nWhen I turn thermostat up , furnace comes on, burners come on, motor that I believe turns blower turns on but i AM NOT GETTING AIR...

have you checked your filter yet? the other thing to check is open the fan door and jumper the door switch,if there is one, and turn the furnace on. is the fan blowing air now?

Mar 22, 2011 | Heating & Cooling

1 Answer

Gas Armstrong Ultra V Tech 91-Is green light supposed to flash?

Installed a new filter and furnace is running great now. The old filter was not that old, but we have been doing some remodeling and I figure that is what clogged it so fast.

Jan 10, 2010 | Armstrong H 67 1PH Bf In Line Circulator...

1 Answer

My furnace is not blowing hot air when I turn on

Normally if you have a limit switch problem on a hot air furnace it is the manual high limit switch that should be located near the blower. If you lost power while the unit was operating the heat build up will trip this switch.
Normally they are about 2 inches round with a red button in the center. Firmly push the button till it clicks.
Sometimes it can be the high limit switch that is just a saftey switch in case the furnace gets too hot.
If you do not have enough air flow this switch will operate excessively and will eventually fail.
The best way to find the problem is to trace the low voltage control circuit till you find the open switch. This can be challenging and time consuming, especially if you are not used to doing it.

I hope that this will help you to solve your problem!

Thanks for using Fixya!!


Dec 09, 2009 | Heating & Cooling

1 Answer

High limit switch open- but only faults in night and extreme cold

Hello , I can try to help you out on this one , It sounds like what is happening is that your exhaust vented up is condensating from the heat in the pipe and the cool in the attic or wherever the exterior of the exhaust pipe travels. It is very common because your exhaust/flu pipe is not insulated.
To fix this issue you must drain the water/condensation from the small 5/16th hoses in front of the blower assembly , just pull them loose and angle them downward to drain. This should fix the problem if this is the problem.
Let me know how it turns out or if you have anymore questions. Phil

Dec 31, 2008 | Heating & Cooling

1 Answer

Armstrong air tech 91 furnace problem

Sounds like the flue is plugged, I had same problem and opened up the draft fan and there was a dead bird restricting the flue. Furnace will never light if the pressure switch never closes as you have found out. Also has anyone moved the switch some are position sensitive meaning have to be in same position factory set the switch. I had one like that also switch was little crooked so I straighten it up and walla worked.

Nov 23, 2008 | Heating & Cooling

Not finding what you are looking for?
Heating & Cooling Logo

Related Topics:

12,133 people viewed this question

Ask a Question

Usually answered in minutes!

Top Heating & Cooling Experts

Paul Carew

Level 3 Expert

3476 Answers

Donni Steen

Level 3 Expert

687 Answers


Level 3 Expert

85206 Answers

Are you a Heating and Cooling Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides