How to find and light or fix the pilot on a gas heater, boiler, furnace, or water heater.

In this article series we provide descriptions and photographs how to select, install, diagnose or repair leaks or operating problems in fuel gas piping, regulators, or controls used on gas fired appliances or heating equipment, addressing both natural gas and LP gas equipment.

Gas Pilot Light Instructions

Here we explain how to identify the type of flame ignition system your gas-fueled heating equipment uses, and then we explain in simple steps how to light the gas pilot on a standing pilot heating appliance. We include notes on what to do if your gas heater uses other types of flame igniters but won't ignite.

Question: How do I re-light my natural gas furnace?

How do I re-light my natural gas furnace (Airco furnace Model #115 AGH). Yes, it is an old furnace. I believe I have gotten a downdraft that has blown out the pilot light.

I am following all the steps that our Natural gas supplier has provided for us.

However, I am not sure which button is the Control Knob.

I do believe the Pilot button is the red one. Please reply. - 2022/09/17,Nellie A. Nikota

This Q&A were posted originally at OLSEN AIRCO HVAC MANUALS & PARTS GUIDES

Illustration above: a Honeywell VR8 type gas control valve for a gas-fueled boiler or furnace used for a gas boiler or furnace used for central heating.

[Click to enlarge any image]

Moderator reply: how to light the gas pilot light or flame on an LP or Natural Gas boiler, furnace, or water heater

I've spent some time looking without success for an old Airco AGH-series gas furnace manual that would have let us confirm exactly which gas control your furnace uses - without success. None of the company's current documents cover that old furnace.

So here are the general steps in lighting a gas pilot light or flame on an LP or Natural Gas boiler, furnace, or water heater that uses a standing pilot - that is, a pilot flame that remains always "on".

General Safety Warnings for Natural Gas, LP or "bottled" or "propane" Gas Installations & Inspections

Immediate LP or natural gas safety hazards: if there is evidence of an LP or natural gas leak at a building, gas odors, for example, you should:

• Do not do anything that is likely to cause a gas explosion, such as lighting a match, operating an electrical switch, or even using a telephone in the building
• Leave the building immediately and keep a safe distance away - 100 feet or more.
• Notify other building occupants of the safety concern
• Contact the local gas company and/or fire department

Heating equipment which the inspector (or building occupant or manager) judges to be an immediate life safety hazard should be shut down and appropriate emergency services called.

Watch out:  improper installation and even improper inspection and testing methods involving natural or "LP" gas can involve dangerous conditions and risk fire or explosion.

Does My Heater Use a Standing Pilot or an Intermittent or Electronic Ignition?

First, look at burner assembly and at the gas valve on your gas-fueled boiler, furnace, or water heater.

Gas boilers, furnaces, water heaters that use a Standing Pilot

Gas heaters that use a standing pilot will have a pilot flame assembly on the burner that includes:

• a gas line feeding to the pilot flame
• a flame sensor that uses either a traditional thermocouple or a newer electronic thermo-sensor hat senses the presence of a flame and closes the gas valve if no pilot flame is found

Above: this is a simple, standing gas pilot assembly such as may be found on gas water heaters and perhaps other gas heating appliances.

[Click to enlarge any image]

The larger-diameter silver tube connects to the gas control valve and delivers LP (Propane gas) or natural gas to the flame outlet.

The smaller-diameter copper tube and gray-silver probe are the thermocouple sensor placed in the path of the pilot flame so as to be heated by the flame.

The other end of the thermocouple connects to the gas valve and will turn off the gas supply if no flame is senses.

Gas boilers, furnaces, water heaters that use Other Burner Ignition Methods - NOT a Standing Pilot

Our illustration below, using a gas pilot light assembly used on some Lennox gas furnaces, shows the key parts that, if present, will indicate that your heater uses a pilot that is NOT a standing pilot - there is an electronic igniter that ignites the pilot flame at the start of a call for heat.

If you do not see a small-diameter tube feeding gas from the control valve to a pilot assembly on the gas burner, and/or if you do not see a standing pilot assembly on the burner, and/or if you see electric wires leading from the gas control valve to an igniter on the gas burner like those shown below, then your heater may use an electronic igniter that creates a small spark to ignite the pilot and burner only when there is a call for heat.

Shown above is a gas furnace pilot burner spark igniter that is commonly used on Bryant, Carrier, Payne and some other gas furnaces. When those furnaces are not running the pilot flame will be OFF.

Look for thin electrical wires leading to a small ceramic device with a tiny metal electrode on the burner or at the pilot light assembly.

Wires rather than a small diameter gas tube between the gas control valve and the burner may indicate either an electronic-igniter that lights the pilot at the start of a burner-on cycle.

 

That furnace or boiler is not a standing pilot type heater.

Or your heater's gas burner may be ignited by a "hot surface igniter" like the Duralight igniter shown below. The hot surface gas burner igniter is used on recent models of Rheem, Ruud, and Weatherking furnaces.

In those cases there is no standing pilot light and instead, if your heater won't turn on, then the igniter or gas valve may need repair or replacement.

Steps in How to Light the Pilot Light on a Gas Heater or Water Heater

Illustration below: the gas control valve for a gas-fueled boiler or furnace used on water heaters.

Usually there are two controls you have to operate to re-ignite a standing pilot light flame controlled by a gas furnace gas-control:

1. Rotate the CONTROL KNOB or DIAL so that the word PILOT is opposite the indicator arrow or triangle. This is the larger control knob and may be black, red, or yellow but it will show the words
   
   OFF - PILOT - ON
   
   Note: See "CONTROL KNOB" in our photo.
   
2. Press and hold the RED "START PILOT" BUTTON down - you might even hear gas entering the pilot but usually not.
   
   This is a "push-down or release" button, not a control knob. It won't have OFF - PILOT - ON marked on it. An example is at upper left in our photo.
3. Hold a lit match or flame close to the gas pilot assembly on the burner until you see the pilot flame ignite.
   
   If your heater has been turned off for a long time you may need to continue steps 2 and 3 for a few minutes to allow time for your gas supply to reach the burner.
   
   If the flame still never ignites, check that your gas supply is turned on and check for a flue-gas spill switch on the heater that may have shut off the control.
   
   See FLUE GAS SPILL SWITCH TRIPPING & RESET
   
4. CONTINUE PUSHING the red PILOT button down for a minute to give time for the thermocouple to heat up - otherwise if you release the red button too early the pilot will simply go out.
5. Release the PILOT BUTTON - the pilot flame should stay lit
6. IF the pilot flame stays lit then turn the CONTROL KNOB to the "ON' or "HEAT" position - that will allow the gas valve to send gas to the burner on a call for heat.
   
   IF the pilot flame will not stay lit and you've waited ample time for the thermocouple to heat up, then there's probably a bad thermocouple that needs to be replaced.
   
   In that case see our Gas Flame Thermocouple Sensors Troubleshooting & Replacement Thermocouple failure causes, replacement methods found
   
   at THERMOCOUPLE REPAIR / REPLACEMENT

 

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2021-04-23 by (mod) - gas water heater pilot flame won't stay lit

@isitold,

Confirm that your gas supply is not blocked

check for a pilot sensor that is not located in the flame

check for a thermocouple that is not securely screwed in to the gas valve

check for flue gas spillage at the water heater draft hood - and a sensor that is turning off the heater - details are
at
FLUE GAS SPILL SWITCH TRIPPING & RESET
and

Watch out: if you find this condition there is risk of fatal carbon monoxide poisoning

IN any event be sure you have working CO detectors properly-located and tested

See more diagnostics at GAS FLAME & NOISE DEFECTS

If none of those obvious causes are present it's time to call a professional

On 2021-04-20 by isitold

brand new hot water heater pilot wont stay lit....

On 2021-01-11 by (mod) - 20 year heat master fireplace burner pilot light troubleshooting

Possibly, but not necessarily. Sometimes even when we replace the thermocouple if we don't make the connection to the gas valve exactly correct and fully tightened or if the sensor is not correctly placed then even with adequate pressure and flow of gas the pilot or burner will not stay on.

If on Lighting the burner you see a normal strong flame that I suspect it's not a pressure and therefore not a regulator issue.

Check also for dirt or debris on the burner

On 2021-01-11 by Mickey

I’ve got a 20 year heat master fireplace. It got to where it would not start or the pilot light would not stay lit. I’ll replace the thermostat valve and the thermal couple.

I’m still having the same problem. Do you guys think all along it could have been the regulator going out?

On 2021-01-05 - by (mod) - gas boiler blows out pilot light

Good news, John and thank you for the feedback as that will help other readers.

Your on-site service technician was a bit more direct and candid than I thought I should be, sitting far away, and only having a bit of text to consider. But I think his or her remarks were spot on.

I see in your photo

debris in the burner tubes

rust in the burner base (possible perforation would foul up air movement)

corrosion at gas regulator fittings

On 2021-01-04 by John W.

Thanks for your help. I am going to get a second opinion on this. The first technician didn't clean or inspect the boiler except to measure the flue CO. Hopefully it's salvageable. Definitely worth the cost of an actual cleaning and inspection.

I mistakenly replied to myself. I have attached a couple of pictures of the burner assembly.

@John W.,
Thank you so much for getting back to me so quickly. I think I should have mentioned that the boiler is 20+ years old (Teledyne Laars JVT75C1).

It has burners like a BBQ with the gas injected into open tubes and no shutters on the tubes.

Would you recommend getting a diagnosis from a different company? Maybe one that doesn't have a sales arm?

On 2021-01-04 by (mod) - gas boiler was blowing out the pilot.

John

First priority is safety, so it makes sense that the tech red-tagged your unsafe heater as a CO hazard.

Disappointing is that there was no diagnosis and repair.

The problem could be improper gas regulator pressure but that's unusual; more-common is an improperly-adjusted air shutter or a combustion air defect.

I would not assume the boiler is in need of replacement before we have a proper diagnosis. Give the service company a call, cite the need for heat and life safety concerns and ask that an experienced tech inspect and diagnose the heater.

Let me know what you're told.

On 2021-01-04 17 by John W.

My natural gas boiler was blowing out the pilot. After relighting, I noticed that the flames on the boiler elements are not 'seated' on the gas outlet holes.

The flames are jumping and making a lot of noise (roaring).

I had it inspected by a (quite young) technician and he red-tagged the system due to high CO in the flue (600ppm). Is it possible that it is just that the gas pressure is too high on the boiler, causing incomplete combustion and high CO readings?

Or is this just the end on my boiler (at a painfully high cost)?

On 2020-10-13 by (mod) - heating furnace gas burner won't ignite after sitting off overnight

Jerry

I don't know what's wrong for sure, Jerry,

a bad thermocouple, a bad thermocouple connection to a gas valve, even a bad igniter or igniter wire or igniter module can all cause the symptom that you describe.

Sometimes when a component is failing it is more-vulnerable to moisture or to low temperature, and it will behave differently once warmed-up.

That can explain why your furnace will re-start OK on subsequent on-cycles but won't start up on its own when it's been off for a longer interval.

I'd consider replacing the control; you might want to take a look at the White Rodgers replacement option for the original 21D18-3 gas ignition system described in this

WHITE RODGERS RETROFIT for WR 21D18-3 GAS CONTROL [PDF]

Near the end of those instructions is a helpful gas burner ignition troubleshooting flowchart that I recommend.

Also see the diagnostic advice

at GAS IGNITER DIAGNOSIS & REPAIR

Shown in our illustration, courtesy of Grainger.com - a supplier - is a White Rodgers cycle-pilot gas ignition system that is a replacement for many White ROdgers OEM gas controls using mercury sensors.

[Click to enlarge any image]

Other readers: see our complete collection of

MANUALS for HEATING & A/C SYSTEM CONTROLS - instructions for controls used on Heating Systems

Or see

MANUALS & PARTS GUIDES - HVAC for a list of heating & air conditioner manuals sorted by brand

On 2020-10-13 by Jerry - Luxaire furnace pilot failure 0- using a White-Rodgers 21D18-3 gas system

Hello.

I have an old Luxaire furnace using a White-Rodgers 21D18-3 gas system.

If the furnace sits idle for any length of time (say overnight) the furnace is unable to produce any spark whatsoever to ignite the pilot.

However, once I light the pilot manually and the furnace runs through a cycle, the furnace can produce a consistent strong spark on subsequent cycles, as long as the furnace has not sat idle for too long between these cycles.

It reminds me of a car with a failing battery. You might require a charge (or a jump) in the morning to get it going, but once started you can run any number of errands, successfully restarting the car a number of times. But let it sit overnight, and in the morning another jump is needed.

This have vexed me for some time and I would be thankful for any guidance.

This Q&A were posted originally at HEATING SYSTEMS - topic home

On 2019-02-09 - by (mod) - do you light the pilot on a Model 55V 50 NRT2 State Industries Water Heater

Donna

Please use the Add Image button to post a photo of the water heater and a sharp closeup of each of its data tags or labels. I ask because looking through State Water Heater manuals I don't fin a model exactly as you've written it.

The concern is nobody wants to give you incorrect instructions for lighting a pilot -a mistake could be dangerous.

You can also call State water heater product support directly at 1-800-365-0024

On 2019-02-09 by Donna

How do you light the pilot on a Model 55V 50 NRT2 State Industries Water Heater

 

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Continue reading  at GAS PILOT WON'T STAY LIT or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• FLUE GAS SPILL SWITCH TRIPPING & RESET
• GAS APPLIANCES, PIPING, CONTROLS
• GAS BURNER FLAME & NOISE DEFECTS
• GAS BURNER SOOT CAUSE & CURE
• GAS BURNER PILOT LIGHT PROCEDURE
• GAS COOKTOP or STOVE IGNITER REPAIR
• GAS BOILER PROBLEMS
• GAS FIRED WATER HEATERS
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• GAS IGNITER DIAGNOSIS & REPAIR
• GAS PILOT WON'T STAY LIT
• GAS PIPING, VALVES, CONTROLS - home
• GAS REGULATORS & APPLIANCE / HEATER CONTROLS - home, Natural Gas regulators & appliance regulators, NG & LP
• GAS WATER HEATER CONTROL VALVES - pilot light, gas valve, thermostat for temperature control
• THERMOCOUPLE REPAIR / REPLACEMENT

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