Furnace Limit Switch | M39029
About this product
Furnace Limit Switch — manufacturer part number M39029.
What this part does
The high limit switch shuts the burners down when the heat exchanger gets too hot. It is a safety device, so when it trips repeatedly the switch is usually doing its job correctly and the real fault is restricted airflow. Check the filter before you replace this.
Replace this part if
- Furnace heats briefly then shuts down, repeatedly
- Blower keeps running after the burners cut out
- Furnace locks out after several failed cycles
- Switch reads open on a multimeter when cold
- Burnt or discoloured switch housing
Specifications
| Manufacturer Part Number | M39029 |
|---|---|
| Condition | New |
| Sold By | Furnace Direct (Hamlin Mechanical LLC, MN Lic. #128688) |
Install difficulty
Easy — about 25 minutes. Tools: 1/4" nut driver, screwdriver. Power off at the breaker: yes. Gas shutoff required: no.
Safety warning: A limit switch that trips repeatedly is a symptom, not the disease. Replace the filter and confirm airflow first. Never jumper a limit switch -- it is the device that stops a cracked heat exchanger becoming a fire.
Typical service life is 8-15 years.
Frequently asked questions
How do I know if my furnace limit switch is bad?
Replace it if you see any of these: furnace heats briefly then shuts down, repeatedly; blower keeps running after the burners cut out; furnace locks out after several failed cycles.
Can I replace a furnace limit switch myself?
Yes. This is a easy repair that takes about 25 minutes with 1/4" nut driver, screwdriver. Always shut the power off at the breaker first. A limit switch that trips repeatedly is a symptom, not the disease. Replace the filter and confirm airflow first. Never jumper a limit switch -- it is the device that stops a cracked heat exchanger becoming a fire.
How long does a furnace limit switch last?
Typically 8-15 years in normal residential use. Heavy cycling, poor airflow, and dirty filters all shorten that.
What if it does not fit?
Return it within 7 days of delivery. If you are unsure before ordering, call (888) 762-1334 — we are licensed HVAC contractors and can confirm the right part for your model.
Sold by licensed HVAC contractors. Furnace Direct is Hamlin Mechanical LLC, Minnesota licence #128688. If this part does not fix the problem, call (888) 762-1334 and we will help you work out what will.
Specifications
| Manufacturer Part Number | M39029 |
| Condition | New |
| Sold By | Furnace Direct (Hamlin Mechanical LLC, MN Lic. #128688) |
| Repair Difficulty | Easy — about 25 minutes |
| Tools You Need | 1/4" nut driver, screwdriver |
| Returns | 7 days on parts |
What this part does
The high limit switch shuts the burners down when the heat exchanger gets too hot. It is a safety device, so when it trips repeatedly the switch is usually doing its job correctly and the real fault is restricted airflow. Check the filter before you replace this.
Replace it if you see any of this
- Furnace heats briefly then shuts down, repeatedly
- Blower keeps running after the burners cut out
- Furnace locks out after several failed cycles
- Switch reads open on a multimeter when cold
- Burnt or discoloured switch housing
Will this fit my system?
This is part number M39029
The number is printed on the part you are replacing — pull the old one and read it, or check the label inside the furnace door. If your number matches, this is the part.
Not sure which part failed? Start from the symptom, or call (888) 762-1334 before you order. We are licensed HVAC contractors and will confirm the right part for your model. If it does not fit, parts can come back within 7 days of delivery.
Not sure this is the problem?
We have written repair and troubleshooting guides for this exact failure. Read the limit switches guides ›
Common questions
How do I know if my furnace limit switch is bad?
Replace it if you see any of these: furnace heats briefly then shuts down, repeatedly; blower keeps running after the burners cut out; furnace locks out after several failed cycles.
Can I replace a furnace limit switch myself?
Yes. This is a easy repair that takes about 25 minutes with 1/4" nut driver, screwdriver. Always shut the power off at the breaker first. A limit switch that trips repeatedly is a symptom, not the disease. Replace the filter and confirm airflow first. Never jumper a limit switch -- it is the device that stops a cracked heat exchanger becoming a fire.
How long does a furnace limit switch last?
Typically 8-15 years in normal residential use. Heavy cycling, poor airflow, and dirty filters all shorten that.
What if it does not fit?
Parts can be returned within 7 days of delivery. If you are unsure before ordering, call (888) 762-1334 — we are licensed HVAC contractors and can confirm the right part for your model.
Commonly replaced at the same time
These fail alongside the part you are looking at.
Get told before the next part fails
One email a week from a working HVAC contractor: the failure we are seeing that week, how to test for it, and what it costs to fix yourself. Filter reminders on your schedule. No discount codes, no countdown timers.
What customers are saying
Saved $2,400 vs local contractor
Got quoted $9,200 from a local HVAC contractor for a furnace replacement. Found Furnace Direct and got the exact same Goodman unit for under $5k delivered. My installer couldn't believe the price and installed it in one day. Runs perfectly.
Fast shipping, exactly as described
Ordered on a Tuesday, pallet arrived Friday. Unit was packed well, no damage, all factory sealed. Andrew answered my sizing question over the phone and got me the right model. Couldn't be happier with the purchase.
Installer said same one he'd buy at supply house
My HVAC guy said he pays basically the same price at his wholesale supply house. The markup contractors add is insane. Furnace Direct cut the middleman out entirely. Will recommend to everyone I know.
Heating my 2,200 sq ft home perfectly
Installed my 96% AFUE furnace a couple months ago. Heats my 2,200 sq ft home perfectly, and my gas bill dropped noticeably compared to the old unit. Great product, great price, great experience from start to finish.
Saved enough to pay for the install
Math was simple: 3 contractor quotes all over $8k. Furnace Direct plus local installer was under $5,500 total. Saved enough to basically pay for the install myself. Quality is identical to what contractors charge a fortune for.
No-pressure, honest pricing
Called a few HVAC companies first — every single one wanted to schedule an "in-home consultation" before giving me a price. Furnace Direct just showed me the price. Bought online, shipped next day, done. This is how it should work.
Questions About This System?
Send a few photos of your current setup and we'll get you a real quote — and let us know if you need installation or just want the unit shipped.
Brands We Carry
Ready for Hassle-Free HVAC?
Premium equipment. One price, in writing. No pressure. No hidden fees.
(888) 762-1334