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What causes the limit switch to open on a Lennox furnace

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6ya6ya
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Posted on Jan 02, 2017

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  • 14 Answers

SOURCE: Fan switch will not make (limit switch).

If the snap switch is not located close enough to the plenum, this can be problem. The other option would be to cover the switch area with a metal shield or liatherm paper (fire rtardant paper).

Posted on Jan 29, 2008

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  • 1 Answer

SOURCE: Lennox Gas Frunace fires goes out, fires goes out, fires goes out

furnace was working fine until the electricity went out for 5 hours now furnace is just humming and then nothing...HELP...

Posted on Dec 29, 2008

  • 86 Answers

SOURCE: Main limit switch

I am providing some information, but I encourage you to have a furnace technician look at your furnace. The reason is; the limit switch trips when there is a problem that may present a fire or combustion hazard. I've seen these switches go bad, but not very often. Usually they are tripping because the plenum is sooted up and excessive heat builds in the combustion chamber. This is common in older furnaces that have pilot flames- the flame runs all year and soot deposits in the plenum, plugging the air flow through the combustion chamber after years of use.

The limit switch is a safety control switch located on the furnace just below the plenum. If the plenum gets too hot, the limit switch shuts off the burner. It also shuts off the blower when the temperature drops to a certain level after the burner has shut off. If the blower runs continuously, either the blower control on the thermostat has been set to the ON position or the limit control switch needs adjustment. Check the thermostat first. If the blower control has been set to ON, change it to AUTO; if the blower control is already on AUTO, the limit switch needs adjusting.

To adjust the switch, remove the control's cover. Under it is a toothed dial with one side marked LIMIT; don't touch this side. The other side of the control is marked FAN. There are two pointers on the fan side; the blower goes on at the upper pointer setting and turns off at the lower pointer setting. The pointers should be set about 25 degrees apart. Set the upper pointer at about 115 degrees Fahrenheit and the lower one at about 90 degrees Fahrenheit.

Posted on Mar 15, 2009

co7196
  • 3433 Answers

SOURCE: open limit switch

Tjere is a limit switch that will only allow the durnace to reach a certain temp by kicking on the fan. The thermostat being unable to read the temp affects its ability to keep the furnace from exceeding your settings. *Advise not to use until corrected. Both limit switch and thermostats are inexpensive and simple to change. If in doubt, call a heat and AC tech to repair.

Posted on May 20, 2009

billyvangogh
  • 108 Answers

SOURCE: miller furnace model M3RL080 BW, code flashes open

Check your furnace filter any Limit fault code usually relates to airflow...Not enough...causes the furnace to run too hot and shut off....the furnace can be too big for your house if its new...the ductwork can be too small , also make sure your return air vents are clean and unobstructed . Your furnace can be running too long a cycle ....also if you have central air conditioning the coil for the AC in the Furnace can be dirty...restricting airflow...if all this seems ok you can usually increase the fan speed or try tunning the fan in the "On" position on your thermostat this will promote better circulation

Posted on Oct 25, 2009

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Bought a house with Lennox G12Q3-82-3 furnace. It doesn't look like electronic ignition. A sticker showing AirMedic Electrostatic Air Cleaner says it was installed 10/1992. Doesn't work.


Here's some borrowed info.:
`These are classic symptom of a limit switch opening. Can't guarantee that is what is going on, but here is some things that can cause the limit switch to open:

1) Low air flow. This can be caused by dirty filter, dirty blower wheel, dirty air conditioning evaporator coil, restricted or collapsed ductwork, blower motor running the wrong direction, blower running on too low of a speed, defective limit switch, or a combination of several of these factors. Inspection along with measuring the temperature rise will find most of them.

2) Heat exchanger failure. Split or burned through heat exchanger

3) Over-fired furnace. If you have eliminated everything in section 1 and 2, and the temperature rise through the furnace is still high, you need to check the furnace to make sure it is not burning more fuel than it is designed to burn. If it is a natural gas furnace, you can check the amount of fuel that is being burned by clocking your gas meter.

Here is a link that will tell you how to use your gas meter to calculate the BTU input of your furnace. It should never be more BTU than the furnace's rated input.
http://www.bacharach-training.com/referpage/clocking_gas_meter.htm

The problems you have could be potentially hazardous. If you are not able to aggressively find the problem on your own, you should hire a professional to look at the furnace immediately. The G12 furnace is getting relatively old. If you have never had it professionally inspected (sounds like you haven't), you probably should have a professional look at it immediately.' END QUOTE
This might cover your problem? don-ohio (:^)

Dec 19, 2016 | Heating & Cooling

1 Answer

Lennox model 80MGF3-75A-2 Furnace will not come on. Where do I start


http://www.ehow.com/info_12194827_led-codes-lennox-80mgf-furnace.html

May 15, 2014 | Heating & Cooling

1 Answer

Lennox lb50527cc


high limit switch, no proof of flame.

Oct 27, 2013 | Goodman Heating & Cooling

1 Answer

My lennox furnace works just fine except that 25% of the time the fan keeps running when it shouldn't and blows cold air


You are using too restrictive of an air filter. If the codes you are getting off the lights says anything about a high limit this is the cause of your blower running all the time. Use a less restrictive filter or have your contractor install a media filter in the system. if you reset the furnace and it does not stop running the blower you have a stuck limit switch and may have to get another or call a service tech to reset it or replace.

Oct 27, 2013 | Honeywell Power Humidifier: Furnace...

1 Answer

Reset limiter switch on Lennox g10 furnace


Try turning the power off to the unit sometimes this works

Mar 05, 2012 | Heating & Cooling

1 Answer

Furnace flashing open high limit


Hello, A limit switch will open when the furnace overheats due to low airflow, . check air filter, clean blower wheel, and check to make sure the blower wheel is running at proper speed and not dragging sometimes cause by a weak capacitor. Anything that restricts airflow will cause a limit switch to open.

Mar 07, 2011 | Goodman Heating & Cooling

2 Answers

Lennox Gas Frunace fires goes out, fires goes out, fires goes out


Check your thermostat anticipator setting. If you dont know how to do this don't try on your own or you may damage your thermostat.

Dec 12, 2008 | Honeywell Electronic Programmable...

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