Quick answer
A water heater pilot that will not light at all is missing spark, gas or air. Confirm the gas valve handle is in line with the pipe, watch the sight glass for a spark when you press the igniter, and hold the pilot button a full minute to purge air after a gas shut-off. A clogged pilot orifice, lint-blocked air intake or tripped thermal cut-off needs a licensed gas technician.
If your water heater pilot won't light at all, with no flame even while you hold the button down, the problem is different from a pilot that lights and then dies. A pilot that drops out is a thermocouple or thermopile story. A pilot that never appears is missing one of three things: a spark, gas at the pilot, or air to burn it with. You can check the first two from outside the heater without a tool.
No spark from the piezo igniter
No spark means no pilot, however much gas is flowing. The piezo igniter is the button that clicks; each press should throw a small blue-white spark at the pilot hood, visible through the sight glass at the bottom of the tank. Dim the lights and look. A click with no spark points to a wire that has slipped off the back of the button, a cracked ceramic insulator on the electrode, or a spark jumping to the wrong spot because the electrode has shifted.
A spark you can see with no flame after it puts the fault on the gas or air side.
No gas reaching the pilot
- Gas off at the appliance valve or the meter. The shut-off on the pipe beside the heater is open when its handle runs in line with the pipe. If the furnace and range are also dead, the supply is off upstream, and that is a call to Enbridge Gas, not a job for a wrench.
- Air in the gas line after a shut-off. After meter work, a new appliance or a tank that has sat with the gas off, the pilot tube is full of air. Hold the pilot button down for a full minute, clicking the igniter every few seconds, before deciding it will not light. Follow the lighting label on the tank; how to relight a water heater pilot walks through it.
- A clogged pilot orifice. The opening that meters gas to the pilot is smaller than a pinhead, and a speck of rust or a spider web blocks it. The spark fires at nothing.
- A kinked pilot tube. The thin tube from the gas control to the burner gets bent when the burner assembly is pulled or something is stored against the heater.
- The control knob not fully on PILOT, or the button not pressed all the way down. After a failed try, turn the knob to OFF and wait the time printed on the lighting label, usually five to ten minutes, so unburnt gas can clear before the next attempt.
No air: the FVIR intake screen and the thermal cut-off
Gas water heaters built since the early 2000s are FVIR designs, short for flammable vapour ignition resistant. The burner sits in a sealed chamber and breathes through a fine screen and flame arrestor at the base of the tank. That screen catches lint, pet hair and dust, and when it clogs the pilot starves for air: it will not light, or it lights weak and yellow and snuffs out.
A heater that shares a room with the dryer is the usual victim, which describes the basement laundry and utility room in a lot of 1970s–90s subdivision homes. Vacuuming the outside of the intake screen at the base is safe homeowner maintenance. Do not poke anything through it.
Starved for air, the chamber overheats and trips the thermal cut-off, a small temperature switch on or near the burner door wired in series with the thermocouple or thermopile. Once it opens, the gas control cannot hold the pilot valve open, so the pilot dies the moment you release the button or never establishes at all. Some heaters have a cut-off with a reset button; others use a one-time switch that has to be replaced. Either way the cause, usually that clogged screen or a venting problem, has to be fixed first.
What you can check on a pilot that will not light, and where to stop
- Gas shut-off handle in line with the pipe.
- Other gas appliances working.
- Spark visible in the sight glass.
- Pilot button held a full minute after any gas interruption.
- Intake screen at the base vacuumed clean, and nothing stored against the heater.
- Status light on the gas control, if it has one. No light at all is normal when the pilot is out, because the pilot powers it; what the blinking light on a water heater means covers the flash codes once it is lit.
Stop there. The burner door on an FVIR heater is gasketed to keep the combustion chamber sealed, and opening it to reach the pilot assembly, orifice or thermal cut-off is work for a technician holding a TSSA G2 gas licence, who will replace the gasket and leak-test afterward. A heater with a power vent or electronic ignition has no standing pilot to light, and its ignition faults are a separate diagnosis.
If you smell gas at any point, stop trying to light it. Do not touch switches, leave the house and call Enbridge Gas at 1-866-763-5427 from outside. A faint whiff right after a failed lighting attempt should clear in a few minutes; a smell that stays is a leak.
What a water heater pilot repair costs
- Diagnosis: $90–$150, deducted from the repair once you say go.
- Thermocouple replacement, when the pilot lights but will not hold: $150–$300.
- Pilot assembly, igniter or thermal cut-off: inside the usual $150–$800 repair band, with a written price first.
- Gas control valve: $400–$600.
- Tank replacement, if the heater is past 10 to 12 years and the repair is a large share of a new one: $1,200–$2,500 installed.
ZK Mechanical is owner-operated by a TSSA-licensed gas technician, and pilot and burner faults on atmospheric tanks are routine water heater repair work for us in Burlington, Oakville, Milton and Hamilton. If the pilot lights but keeps dropping out, why a water heater pilot keeps going out is the better page. Otherwise call (647) 801-1252 or book a repair visit.