Mr Buddy Heater Pilot Lights But Not Burner
You press the knob, hold it, click the igniter. The pilot lights. It stays burning.
Then you turn the knob to "On" and nothing. The main burner never fires.
That is the exact scenario this article covers. It is one of the most common problems with these portable propane heaters. Nine times out of ten, a single part fails.
It is not a catastrophic valve or a tank issue. As of 2026, the Mr. Buddy line models MH9BX, MH18B, and the Big Buddy still use the same safety system.
A thermocouple keeps the pilot lit. A thermopile opens the main gas valve. Per ANSI Z21.11.2 standards, the thermopile must generate at least 300 millivolts before the main burner will fire.
That number is your ticket to a fast diagnosis.
Image source: Bing (Web (fair-use with source credit))
Quick Answer
The pilot stays lit. The burner does not. The part that opens the gas valve is a thermopile.
A bad thermopile is the most common cause. It generates too low a voltage.
Test it with a multimeter. Target is 300 to 750 millivolts.
Below 300 Replace the thermopile. Above 400 but still no fire Check gas pressure.
That is the short fix. The rest is detail.
Why Your Mr. Buddy Pilot Lights but the Burner Doesn't
Your Mr. Buddy has two different safety devices. The thermocouple keeps the pilot gas flowing.
If that fails, the pilot goes out when you release the knob. If the pilot stays lit, the thermocouple is fine.
The thermopile sits next to the thermocouple. It is a larger cylinder that heats up from the same pilot flame. That heat generates a small electric current measured in millivolts.
That current tells the gas valve to open for the main burner.
When the thermopile gets dirty, corroded, or simply wears out, its voltage drops. The gas valve does not get the signal it needs. The pilot burns, but nothing else happens.
Aggregate user reviews and manufacturer documentation confirm this as the top failure point. It is not a design flaw. It is a consumable part.
Like a bulb that dims before it dies.
The 3-Step Diagnostic Workflow: Find the Real Problem
Step 1: Confirm the pilot stays lit after releasing the knob
Turn the control knob to "Pilot." Press and hold it. Light the pilot. Keep holding for 60 seconds.
Then release.
If the pilot goes out, you have a thermocouple problem. That is a different article. If the pilot stays burning, move to Step 2.
Step 2: Watch the pilot flame color and coverage
Look at the flame while the pilot is running. It should be blue, steady, and reaching about 3/8 to 1/2 inch tall. It must directly touch the silver tip of the thermopile.
If the flame is yellow, lazy, or flickering, the pilot orifice is probably clogged. Spider webs and dust are common culprits. Clean the orifice before doing anything else.
If the flame is blue but too short or not reaching the thermopile, you may have low gas pressure or a misaligned thermopile.
Step 3: Test the thermopile voltage with a multimeter
Set your multimeter to DC millivolts. Disconnect the thermopile wires from the gas valve. Connect the meter probes to the two thermopile terminals.
Polarity does not matter.
Light the pilot and let it run for 60 seconds. Read the voltage.
Under 300 mV Replace the thermopile. Between 300 and 400 mV It may work intermittently. Over 400 mV and the burner still will not light The problem is elsewhere.
Likely the gas valve, regulator, or propane pressure.
Image source: Bing (Web (fair-use with source credit))
Step-by-Step Fixes for Each Diagnosis
Fix 1: Replace the Thermopile
Buy a compatible thermopile. Part F273741 or equivalent costs $15 to $25. Turn off the gas and let the heater cool.
Remove the outer casing. Unclip the old thermopile from its bracket. Disconnect the wires.
Install the new one in the same position. The tip must sit exactly where the pilot flame will hit it. Reconnect wires, reassemble, and test.
A quick trick While the heater is still assembled but disconnected from gas, manually hold the pilot button. See if the gas valve clicks when you turn to "On." That tells you the thermopile is delivering voltage. If it clicks and the burner fires after reassembly, the fix worked.
Fix 2: Clean the Pilot Orifice
Shut off the gas. Remove the pilot assembly cover. The pilot orifice is a tiny brass fitting at the base of the pilot tube.
Use compressed air to blow it out. If that does not work, use a fine wire. A single strand from a wire brush works.
Gently clear the hole. The orifice is about 0.007 inches. Do not enlarge it.
Reassemble and relight. The flame should turn blue.
Fix 3: Check Propane Pressure and Flow
If the thermopile tests good and the pilot flame looks correct, the issue is gas supply. Try a fresh 1 lb tank first. For 20 lb tanks, check the hose for kinks and the regulator for freeze-up.
Some hoses have a built-in regulator that can clog with debris. A hose filter sold by Mr. Heater solves that.
If the burner lights on low but not high, you almost certainly have a pressure problem.
Image source: Bing (Web (fair-use with source credit))
Common Mistakes That Waste Your Time
Replacing the gas control valve too early. That is a $40 to $60 part plus labor. Thermopiles are $15 and fail far more often. Test before you replace.
Over-tightening gas connections. Hand-tight plus a quarter turn is plenty. Stripped threads cause gas leaks.
Cleaning the main burner orifice instead of the pilot orifice. They are different parts. The pilot orifice is tiny and clogs first. The burner orifice rarely clogs unless debris falls into the burner tube.
Skipping the multimeter test. Guessing costs time and money. A $10 multimeter pays for itself in one diagnosis.
Using the heater indoors after disassembly without leak-testing. Any time you open the gas system, use a soap-and-water leak check. A propane leak in a confined space is a serious carbon monoxide and fire risk. Follow NFPA 58 safety guidelines for portable propane appliances.
Quick-Reference Specs & Test Values for DIY Diagnosis
| Component | Expected Value | Action if Below |
|---|---|---|
| Thermopile voltage (pilot on) | 300-750 mV DC | Replace if under 300 mV |
| Thermocouple voltage | 20-30 mV DC | Replace if under 10 mV |
| Pilot flame height | 3/8 to 1/2 inch | Clean orifice or adjust pressure |
| Pilot orifice size | About 0.007 inches | Clean gently with fine wire |
| Propane gas pressure at valve | 11 inches water column | Check tank and hose |
| Hold time after lighting pilot | 60 seconds minimum | Hold longer on cold start |
Keep these numbers handy. They turn a frustrating guess into a 10-minute repair. Most of the time, a fresh thermopile and a clean pilot orifice are all you need.
Frequently Asked Questions
Why does my heater work on low but not on high?
This is almost always a gas pressure problem, not a thermopile issue. A weak or freezing regulator, a nearly empty tank, or a long hose can deliver enough gas for low fire but not for high. Try a fresh 1 lb tank first.
Can I use a 20 lb tank without a filter?
You can, but you should not. The long hose on a 20 lb setup can accumulate debris from the tank valve. That debris clogs the heater internal regulator.
A Mr. Heater hose filter catches that before it reaches the heater.
How do I know if the gas control valve is bad vs the thermopile?
Test the thermopile voltage first. Above 400 mV and the burner still will not light The valve is likely bad. Below 300 mV The thermopile is your problem.
Replacing a valve is more expensive and requires disconnecting gas lines. Start with the cheap test.
Will a dirty burner tube cause the pilot to light but not the burner?
No. A dirty burner tube affects flame quality and may cause yellow flames or sooting. It will not prevent the burner from lighting.
If the pilot ignites but the burner will not, the blockage or failure is in the pilot assembly, the thermopile, or the gas supply.
How often should I clean the pilot assembly?
Once a year is good for regular use. If you store the heater in a dusty garage or shed, clean it twice a year. Spider webs are the biggest culprit.
A quick blast of compressed air before each season prevents most problems.
Troubleshooting Decision Flow
Pilot will not stay lit Replace thermocouple.
Pilot stays lit, burner will not fire. Test thermopile voltage with multimeter.
Thermopile below 300 mV. Replace thermopile.
Thermopile above 400 mV, burner still will not fire. Check gas pressure. Try fresh 1 lb tank.
Pilot flame is yellow or lazy. Clean pilot orifice with compressed air or fine wire.
Pilot flame is blue but too short. Check for low propane or misaligned thermopile.
Burner lights on low but not on high. Gas pressure problem. Check regulator and hose filter.
Burner lights but goes out after 30 seconds. Thermopile is borderline. Replace it.
That is the full workflow. Start with the multimeter test. It saves time, money, and frustration.
Similar Posts
