Gas Dryer Ignition System Repair Standard

Purpose

Three different parts produce the same complaint on a gas dryer: it tumbles and will not heat. The glow-bar igniter, the gas valve coils and the flame sensor each fail into that sentence, and a shop that guesses replaces two of them on the way to the right one. Worse, the part that actually failed is sometimes a limit that opened for an airflow reason nobody looked for, and fitting a new one restores heat to a machine that will open it again.

This standard puts one full observation of the ignition sequence in front of every parts decision, requires a root cause for any open limit, and closes with a leak test and a carbon monoxide check on every visit where a gas joint was broken. The leak test is the part that turns a repair into a repair somebody can defend.

Scope

Residential and light-commercial gas clothes dryers on a no-heat, intermittent-heat or ignites-then-drops complaint: the igniter, gas valve coils, flame sensor, radiant sensor circuit and the gas connection at the appliance.

It does not cover electric heat, which the dryer heating fault repair standard owns, the drum drive, or the vent cleaning that step 5 routes to. Work upstream of the appliance shutoff, including the flexible connector's supply piping, is a licensed gas fitter's scope in most jurisdictions.

Roles and the handoff between them

Before the truck door closes on this call

Gas odor ends the diagnosis before it starts. If anyone smells gas on arrival or during the work, everybody leaves the building immediately, no switch is touched, no light is turned on or off, no phone or radio is used inside, the door is left as it is, and the gas utility and the shop are called from well clear outside. Nobody goes back in to find the leak. That instruction is not a caution attached to a step, it outranks every step below.

Wear a personal carbon monoxide monitor and commit to an action level. OSHA's general industry permissible exposure limit for carbon monoxide is 50 ppm as an 8-hour time-weighted average at 29 CFR 1910.1000 Table Z-1, and NIOSH publishes a 35 ppm recommended exposure limit on the same averaging basis. Those are worker exposure limits, not house-air standards, so the shop default is stricter: at 35 ppm on the monitor, stop the appliance, ventilate and re-check; on any alarm, everyone leaves and the fire department or gas utility is called from outside.

Isolate electrically and by fuel, separately. Unplug the dryer and close the appliance gas shutoff. The cord-and-plug provision at 29 CFR 1910.147 holds only while the plug stays under your exclusive control; work practices for anything metered live are 29 CFR 1910.333(b)(2), and a circuit taken as dead is proved on a known live source before and after per NFPA 70E-2021, 120.5.

The procedure

1. Check the air before you check the appliance. With the monitor on and the room as found, note any gas odor and the CO reading before anything is run. Acceptance: no gas odor and a stable monitor reading below the 35 ppm action level. Wrong looks like an odor dismissed as "the neighbor's grill." Stop rule: any gas odor takes the leave-the-building instruction above; any reading at or above 35 ppm stops the work and ventilates before anything else. Hazard is the atmosphere itself, so the monitor is on the tech, not on the dryer.

2. Isolate both energies and confirm both. Unplug the dryer and close the appliance shutoff, then confirm the valve handle position by sight rather than by feel. Acceptance: plug under your control and the shutoff handle visibly across the run of the pipe. Wrong looks like a quarter-turn valve assumed closed because the handle moved. Stop rule: a shutoff that is seized or leaks past stops the visit and goes to a gas fitter. Hazard is a stuck valve forced with a wrench, which snaps at the body; it turns by hand or it does not turn.

3. Watch one complete ignition sequence before naming a part. Restore gas and power, start a heated cycle, and watch through the burner port from the side: igniter glow, coils pulling the valve open, light-off, the sensor dropping the igniter, and the flame holding through a cycle. Acceptance: each stage happening within the timing the tech sheet gives, and the stage that fails written down. Wrong looks like a tech who saw no flame and ordered an igniter without knowing whether the bar ever glowed. Stop rule: a flame that lights and then drops repeatedly is a sensor or limit story, not an igniter, and goes to step 4 on that circuit. Hazard is an open cabinet on a firing appliance and a delayed ignition that puffs out of the port, so the observation is made from the side with the face out of line with the port, sleeves clear of the burner, and nothing resting on the burner tube.

4. Dead-test the stage that failed. Shut the gas, unplug, prove dead, then test the igniter for continuity, both valve coils against the tech sheet's values, the flame sensor for a closed circuit at room temperature, and the thermal fuse and limits. Acceptance: igniter continuous, both coils inside the sheet's bands, flame sensor near zero ohms cold, fuse and limits closed. Wrong looks like a flame sensor open at ambient, which stops the igniter circuit and reads exactly like a dead igniter. Stop rule: a reading outside the sheet's band condemns that part only; nothing else on the list gets replaced on suspicion. Hazard is a burner assembly still hot from step 3, so it is left to cool and handled by its bracket.

5. Give any open limit a cause before you touch it. For an open thermal fuse, cutoff or hi-limit, name the reason: blocked vent, crushed transition duct, failed blower, or a cycling thermostat that stopped opening. Acceptance: an observed cause written on the ticket. Wrong looks like a fuse fitted and the machine handed back, which is the sentence that precedes both the second call and the fire. Stop rule: no cause, no fuse, and the airflow work in the dryer vent standard runs first. Hazard: none here, the gas is off and the machine unplugged.

6. Fit the part, remake the joint, and leak test it before anything fires. Replace the condemned component, and where a gas joint was broken remake it with a connector listed to ANSI Z21.24 that has not been reused, with joint compound rated for the fuel gas on the male threads only, then open the shutoff and test every disturbed joint with a leak detection solution or a listed combustible gas detector, the approved methods under NFPA 54 (ANSI Z223.1), the National Fuel Gas Code, in the edition your authority having jurisdiction has adopted. Acceptance: no bubble growth at any joint over a full minute and no detector response. Wrong looks like a joint checked by nose, which finds a leak only after it is big. Stop rule: any bubble or detector response means the gas is shut off at the appliance and the joint is remade; never chase a leak with a flame, and never tighten a leaking flare under pressure. Hazard is released fuel gas in an enclosed laundry room, so the room is ventilated during the test and no ignition source is operated while a joint is open.

7. Relight, verify two cycles, and re-check the air. With panels on, run a heated cycle through at least two complete ignition events, then re-test the joints under operating conditions and read the monitor again with the dryer firing. Acceptance: a stable blue flame with no lifting or yellow tipping, the igniter dropping out after light-off both times, no leak indication at any joint, exhaust damper held open at the hood, and the monitor below the 35 ppm action level with the machine running. Wrong looks like one good light-off accepted as proof, when the second attempt is where a weak sensor shows up. Stop rule: a lazy or yellow flame, an igniter that stays glowing, any leak indication, or a rising monitor reading takes the machine out of service with the shutoff closed and the customer told not to use it. Hazard is a firing appliance with the customer present, so they stay out of the laundry room until the panels are on and the readings are taken.

The record this produces

A gas ignition worksheet on the ticket:

• Air on arrival: gas odor answer and the CO reading before work.
• Sequence observation: which stage failed, and the timing seen against the sheet.
• Dead tests: igniter, both coils with the bands compared against, flame sensor at ambient, fuse and limits.
• Root cause: for any open limit, in plain words.
• Gas work: which joints were broken, the connector fitted, the leak test method, and the result at each joint.
• Return to service: flame character, two ignition events, damper behavior, and the monitor reading with the dryer firing.

The leak test method and the monitor reading are the two fields an insurer, a landlord or a gas utility investigator will ask for, and they cannot be reconstructed after the fact.

One run of this procedure, filled in

Gas dryer, about 6 years old, tumbles and will not heat. Interior laundry closet off a hallway.

• Step 1: no gas odor on arrival. Personal monitor steady at 0 ppm, well under the 35 ppm action level.
• Step 2: unplugged, plug on the washer lid. Appliance shutoff closed by hand, handle visibly across the pipe run.
• Step 3: gas and power restored, heated cycle started, watched from the side. The glow bar came up and glowed within the timing the tech sheet gives. The coils never opened the valve, so there was no light-off. Failing stage recorded as the valve or its circuit, not the igniter.
• Step 4: gas shut, unplugged, proved dead both ways. Igniter continuous. Booster coil inside the sheet's band. Secondary coil read open. Flame sensor near zero ohms at room temperature, thermal fuse and both limits closed. One part condemned, the coil kit, and nothing else touched.
• Step 5: no limit open, so no root cause work was owed. Vent condition still checked and noted as clear, since a restriction would have shown up as an opened limit later.
• Step 6: this step failed the first time. Coil kit fitted, the valve union remade with a new connector listed to ANSI Z21.24 and compound on the male threads only. Leak test with approved solution showed slow bubble growth at the union over the first minute. Stop rule taken: shutoff closed, pressure released, joint disassembled and remade with the flare face cleaned and the connector reseated, then re-tested. Second test showed no bubble growth over a full minute at any of the three disturbed joints and no detector response.
• Step 7: panels on, heated cycle run through two complete ignition events. Both lit within the sheet's timing with a stable blue flame, no lifting, no yellow tipping, and the igniter dropping out after each light-off. Joints re-tested under operating conditions with no indication. Damper at the hood held open. Monitor read 0 ppm with the dryer firing.

The second test covered all three disturbed joints, not only the one that leaked: a joint that was fine before a union came back apart is not still proved.

References

• NFPA 54, the National Fuel Gas Code (ANSI Z223.1), in the edition your authority having jurisdiction has adopted, which binds the installation and reaches you through the permit, for connection and leak-check practice.
• ANSI Z21.24 / CSA 6.10 for appliance connectors, which are not reused once removed.
• 29 CFR 1910.1000 Table Z-1 for the OSHA carbon monoxide permissible exposure limit, alongside the NIOSH recommended exposure limit.
• NFPA 70E-2021, 120.5 and 29 CFR 1910.333(b)(2) for the proving sequence and work practices on the electrical side, with 29 CFR 1910.147 for the cord-and-plug isolation.
• See related: the dryer heating fault repair standard, the dryer vent inspection and cleaning standard, and the gas range connection and leak check standard.