Sooty gas burner (C) Daniel Friedman Diagnose & Repair Gas Igniters
Stoves, Water Heaters, Furnaces, Boilers

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Gas igniter troubleshooting on heating equipment:

This article explains the cause, diagnosis, and cure of gas heater or gas appliance igniter problems that cause bangs, whooshes, noises, clicking, or failure to ignite properly.

Here we discuss: . Causes of gas top range burner to fail to ignite. Causes of short circuiting in cookstove electrical wiring.

Repair methods for gas burners that won't ignite. Repairs for furnace or boiler gas burner igniters that won't stop clicking. Diagnose and repair loud bang or whoosh when boiler or furnace gas burners igniters. Watch out: some of these conditions are dangerous.

We also discuss both gas igniters and gas regulators on gas fired heating equipment and LP or Natural Gas Pressure Regulators used on building appliances such as gas fired furnaces, boilers, water heaters, and stoves.

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Diagnose & Repair Bad or Noisy Gas Burner Igniters

Window Air Conditioner that fell (C) Daniel  FriedmanThis article series provides descriptions and photographs of unsafe gas piping, regulators, or controls on heating systems, indications of unsafe or improperly operating gas appliances, gas meters, and other gas installation defects.

This document also provides free sample draft home inspection report language for reporting defects in oil and gas piping at residential properties.

[Click to enlarge any image]

Photo at left: the igniter module for a Jenn-Air countertop gas cooktop. We replaced this item as well as the wiring and individual igniters to cure chronic gas burner ignition problems: endless clicking. Details of that repair are found in the article below.

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

If you smell gas you should leave the building immediately and should do so without doing anything that could create a spark such as operating a light switch or telephone. From a safe location, call your gas company's emergency line and/or your fire department. The text provided here is a working draft and may be incomplete or inaccurate

Question: Noisy gas burner igniter worry: when the valve opens it sounds like a hammer hitting a metal pipe

Photograph of a gas regulator showing detailsBoth times InspectAPedia has warned me about possible errors I avoided by reading your website on Furnace Inspection. You've heard it many times I'm sure, but thanks for the heads up.

Many times I've learned the expensive way what not to do in DIY project.

May I ask your opinion on intermittent pilot valves for gas furnace? My furnace works perfectly. However, when the valve opens it sounds like a hammer hitting a metal pipe..

Is it possible the electronic ignition is sending more than 24 volts to the valve solenoid and that's why it makes such a loud noise on opening?

There's a box that regulates and sends the 24 volt electronic signal to the pilotless ignition that I've thought about replacing.

About your pro bono advice, I'm 60 years old, no job, no pension and would appreciate any advice. - R.K., MI

Reply: Short answer: the gas burners may need cleaning, the system may be unsafe, you need a service call

Sooty gas burner (C) Daniel FriedmanA competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem, but it sounds to me as if you are on the right track. Sort-of.

First we ought to rule out a dangerous noise that can be heard when the gas furnace ignites.

Properly when the thermostat calls for heat the igniter lights a pilot that then ignites gas when it is released into the burners.

If burners are dirty or clogged, the gas flame may not be igniting across all of the burner tubes as quickly as it should. A result could be incomplete ignition and a banging sound when the accumulated gas finally ignites.

You should be able to detect this problem by observing with care just what happens during a heater on-cycle.

Watch out for sooty gas burners: If you see soot on or around gas burners such as shown in our photo (above) you should shut off the equipment (it is unsafe) and call a heating service technician promptly.

And if this is the problem, a service call that includes cleaning rust and debris off of the pilot and igniter, or rust and debris off of the burners and checking their adjustment might fix the trouble.

If the gas burner tubes include flame crossover slots, those are intended to assist the spread of flame from the first ignited gas burner tube over to the other tubes. Be sure those slots are cleaned as well. Be sure to also ask your service tech to check the proper operation of all of the heater safety controls while s/he is there.

Watch out: in boiler school our instructor came to class one night with his previously full-beard shaved off. His eyebrows looked odd too. He explained that he was kneeling by the burner, watching too closely when the flame was igniting. A flashback burned off half of his beard and one eyebrow. He had to finish the job himself with a razor.

Don't get your face too close to the gas burners while inspecting for trouble during flame ignition.

There might be a different problem, a delay in igniting the pilot itself, though that is probably less common.

What Causes the Bang, Kaboom, or Loud Whoosh When the Gas Burners are Igniting?

A "bang" or "kaboom" (as some folks describe it) sounds very dangerous, if that's what you've got. It can signal that you are getting "delayed ignition" of the gas in your combustion chamber. If the gas valve opens and sends gas through the burners but actual ignition is delayed, gas accumulates, then ignites with an explosion when the spark finally occurs.

The risk is a damaged, cracked heat exchanger leading to a costly furnace replacement, or worse, a dangerous heating system leaking potentially fatal carbon monoxide into the building.

A loud "whoosh" during burner flame ignition may be caused by the same burner clog and debris problem, especially if it's heard earlier in the development of this dirt and debris difficulty.

Photograph of  this gas flame which gives a clue that there may be an operating problem and an unsafe gas furnace in this buildingWatch out: for questionable advice we've come across when researching the noisy gas burner ignition worry: advice that focuses on adjusting the burner air shutter to improve the flame may be confusing a dirty burner problem (discussed just above) with the need for proper burner adjustment.

The two could be related: if there is a shortage of combustion air the burners could be producing a bit of soot that in turn clogs the burners and leads to a bang or whoosh sound when the gas furnace or boiler burner ignites.

But if the root problem was improper combustion air to the heater or improper air mix adjustment at the burner tubes themselves, that problem would have probably been present from day one of the heater's installation.

If your heater has worked well for some time and now is developing noise, check the advice we gave at the start of this note.

Watch out: a heating appliance might have adequate combustion air only when the utility room door or some other nearby door is open. If the service tech adjusts and tests the system with the door open, the system may look just fine.

But when s/he leaves and shuts the door to the utility room there might be inadequate combustion air.

Details about diagnosing and correcting gas or oil appliance combustion air problems are at COMBUSTION AIR DEFECTS

Watch out: also for the presence of soot anywhere in, on, or around the gas burners. If the system is producing visible soot its operation is improper and very dangerous as production of potentially fatal carbon monoxide is probably going on.

While natural gas and LP gas normally burn clean, a chimney or draft or combustion air problem can lead to very rapid system clogging, soot, and potentially fatal heating system troubles.

Sources of Heating System 24V Transformer Noise

Question: [continued] My first note should have mentioned that I narrowed the hammer on a pipe sound to the actual valve by shutting off the natural gas supply and reproducing the sound without an actual ignition. However, I would guess you answered my question on improper voltage going to the ignition because your note did not even mention that as a possible issue.

I did replace the valve last fall. New Honeywell equivalent valve. You guessed it same issue. Maybe even a little more noisy than the 20 year old original. I will look into a transformer replacement.


I have never seen a heating system coil develop a defect that led to high voltage coming out of a furnace or boiler 12V or 24 V transformer, so I didn't suspect that cause.

According to our electrical expert Paul Galow (Galow Consulting), the transformer is very unlikely to be the root cause of the sound you describe, and a more likely cause, if you have indeed traced the sound to the valve itself, is a mechanical problem in the valve that means it needs replacement.

The output voltage of a transformer is determined by the input voltage and the number of wire turns in the transformer winding. To double the output voltage of the heating system 24V output transformer you'd need to have cut or shorted the transformer in a way that eliminated half of those turns.

Such a defect would be not only unusual but it would more likely lead to burn-up of the device and it would stop working altogether. You could replace the 24V transformer as an experiment - they are quite inexpensive, but it doesn't sound as if the trouble lies there.

Transformers do make noise, but more likely they make a 60-cycle buzzing or humming sound. The transformer often has a core made up of laminated metal components. If the glue fails the core can vibrate, causing a hum.

So while we don't rule out some bizarre defect that causes the transformer to send an overcurrent to the gas valve mechanical solenoid that opens to actually send gas to the burners, it's not likely and more likley is wear or something breaking inside the mechanical parts of the solenoid itself.

Now to the Gas Solenoid Valve Itself

With all those safety warnings and dirty burners out of the way, if you do not see any burner troubles and you can trace the clicking hammering noise really right to the gas solenoid valve, it probably needs replacement.

As you have made clear that you are hearing a loud hammer-click that seems to come right from the gas solenoid valve itself, it sounds as if there lies a mechanical defect.

We [DF] fixed a humming transformer by whacking it once with a hammer. Not very elegant and certainly not recommended by a repairman, but the humming quit for another year or so. About replacing the solenoid valve, given that your previous replacement didn't last: It's a bit subtle but

Watch out for Batches of Bad HVAC Replacement Parts

Watch out: I [DF] have bought and replaced heating and air conditioning system replacement parts (and for that matter car parts) only to find the new parts were defective. Worse still is to go back to the same store, buy another new part, only to find it's defective too.

Keep in mind that often all of the replacement parts of a given part number that are stocked at a local supplier often arrived in the same box, on the same day, and came from the same production run. So if one of them is bad, sometimes all of them are.

Try buying the part somewhere else when you replace it, or check the lot numbers on the package to see if you can get a part from another production run.

See GAS REGULATORS for APPLIANCES for details on how to inspect and test LP or natural gas regulators and controls.

Diagnose & Fix Gas Igniter Problems on Stovetops

Photograph of a natural gas regulator on a furnace

When a gas-fired heating appliance stops working the problem may be with the igniter, not other gas valve components.

Our photo (left) shows an LP gas stove top burner igniter sparking away.

Watch out: we disassembled the stove top burner to make this photo. But don't turn on your gas stove with burner parts missing - the flame won't ignite properly and you could cause a dangerous gas explosion.

Start by checking the wire connected to the igniter itself. If the connection is loose or damaged that could be the problem.

If the ceramic igniter is cracked or damaged it may be shorting to ground and unable to ignite the gas flame.

We have seen recurrent problems with some stove-top gas igniters whose wires ran across the interior pan of the stovetop where they rested in water or cleaners used to clean that appliance.

The result was a shorted igniter wire and constant clicking that drove the homeowners crazy.

Details about how we diagnosed & repaired this problem are at GAS COOKTOP IGNITER REPAIR - in that article also see GAS IGNITER CLICKING DIAGNOSIS for detailed diagnosis and repair suggestions for clicky gas burner igniters.

If you are having trouble removing an old cooktop gas igniter to replace it with a new one, see GAS IGNITER REMOVAL where we use a Jenn-Air gas cooktop igniter as an example.

The gas igniter control module may itself fail and need replacement. This is a more costly part, and in our experience is less often the problem than the items above.


Continue reading at GAS COOKTOP IGNITER REPAIR where we discuss the diagnosis & repair of gas igniters on cooktops & gas ranges or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see GAS IGNITER DIAGNOSIS FAQs - questions & answers originally posted at this article


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GAS IGNITER DEFECTS & REPAIRS at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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