Pilot Light Goes Out in Cold Weather

The Short Answer: A pilot that holds in May and dies on a 20°F windy night is draft, LP that will not vaporize, a sealed closet, or a packed FVIR screen — not a thermocouple that failed with the calendar. Relight once per the jacket. If it dumps again when the wind or the dryer starts, stop. Hire a licensed plumber.

Search Intent & The Real Problem

You relight it at 7 a.m. It is dark again at 7 p.m. The $12 thermocouple you installed in October is not “wearing out in the cold” on a schedule. Cold air down an uncapped chimney blows the flame off the tip. A house shut tight for winter, with the bath fan and dryer running, steals the draft hood. Propane in a 20-lb cylinder at 0°F does not feed a 35–40 kBTU tank plus a furnace. Lint packed in a post-2003 FVIR arrestor chokes the burner worse when every window is closed.

This is not the generic will not stay lit page. That is year-round dropout. This page is weather-tied. If the main fires then drops while the pilot holds, you want burner won’t stay lit.

What other guides get wrong

They start with sandpaper on the thermocouple. A sensor that held all autumn did not forget how to make 20–30 mV because it snowed. They tell you to “bleed the LP tank” or crack a union for air. Air is an install problem, not a January ritual — do not purge it yourself. They skip combustion air and the dryer. They also confuse condensate dripping on the pilot with a “bad thermocouple” — water on the pilot.

Step-by-Step Troubleshooting

Step 1: Prove it is weather, not a dead magnet

• What to look for: When it dies versus wind, exhaust fans, and LP level. Photograph the vent cap and the rating plate.
• Required tools: Calendar and eyes. The jacket lighting card for one relight only.

Step 2: Draft hood, vent, and wind — before parts

• What to look for: Missing or rusted chimney cap. Vent that ends under a soffit or next to a ridge that dumps wind down the pipe. Tissue at the draft hood with the main on: it should pull in, not flap out. Spillage is not “white smoke” you ignore. Snow or ice over an outdoor termination on a power-vent or tankless is a different machine; on a natural-draft tank it is the cap and the storm.
• Required tools: Eyes, a tissue. Gas off if it is spilling.

A perfect thermocouple cannot hold a flame the chimney is extinguishing. If it spills, shut the appliance cock.

Step 3: Closet combustion air and the dryer

• What to look for: Heater in a sealed closet with the louvered door replaced by a solid slab. Foam weatherstrip on the utility-room door added last fall. Dryer, bath fan, and range hood on a tight house — classic winter negative pressure. Garage unit with the overhead door weatherstripped and a running car. You need combustion air; a 40 kBTU tank is not optional about that.
• Required tools: Eyes on the door and the vents. Do not “fix” this with a window cracked next to the draft hood.

If the pilot dies the moment the dryer starts and returns when you kill the dryer, that is air, not a sensor.

Step 4: LP vaporization and regulator freeze — still not a DIY purge

• What to look for: Other LP appliances starving at the same time. Regulator frosting or icing. A 20-lb cylinder feeding a cabin heater. Propane tank pressure falls with temperature (roughly ~40 psi at 20°F, ~28 psi at 0°F, ~11 psi at -20°F — the tank still has liquid; it will not vaporize fast enough). Buried or unburied tanks, empty below ~20%, or a first-stage regulator full of moisture will look exactly like a thermocouple.
• Required tools: None on the fittings. Gauge the tank percent. A licensed tech’s manometer: typically 10–11 in. w.c. LP at the appliance (confirm the plate). Natural gas winter problems are almost never “the meter froze”; they are draft and air.

Do not crack the pigtail. Do not heat a tank with a torch. If the stove will not light either, call the LP supplier, not a water-heater parts cart.

Step 5: FVIR lint, condensate, and the one legitimate sensor check

• What to look for: Dust mat under a post-2003 natural-draft tank — the flame-arrestor at the bottom. Winter = more dryer lint, more pet hair, doors closed. Pilot that leans off the thermocouple tip in a draft. Water dripping from the draft hood onto the flame after a long recovery (flue condensate in a cold chimney). Rust in the burner tray is a tank, not weather — bottom leak.
• Required tools: Flashlight at the base. Vacuum around the jacket from outside. Do not pull an FVIR burner door if you cannot reseal it.

If millivolts are in spec with a sharp blue pilot wrapping the tip and it still dies only when the wind hits, you do not need a second thermocouple. You need draft or air. Brand-specific hold problems: Rheem pilot.

When DIY Ends: Calling a Licensed Pro

Stop at gas odor, spillage at the draft hood, a scorched combustion door, FVIR chamber service, and any vent that needs a cap, a liner, or a new termination. You may relight once per the jacket, look for lint at the arrestor from outside, confirm LP percent, and notice that the dryer kills the pilot. You may not tent the draft hood, loosen fittings, or jumper the sensor. A licensed plumber will prove draft with the main on, measure millivolts, and tell you whether this is a $12 screen cleaning or a chimney that was never legal.

Frequently Asked Questions

Q: Why does my water heater pilot light go out in cold weather? A: Wind down the vent, negative pressure from exhaust fans, a sealed closet, LP that will not vaporize, a packed FVIR screen, or condensate dripping on the flame. A thermocouple that held all fall is rarely the first part.

Q: Can cold weather ruin a thermocouple? A: Cold draft can blow the flame off the tip so the magnet drops. The part is often still good. Fix the draft. If it will not hold on a calm day either, then you are on the generic stay-lit path.

Q: Should I keep relighting a pilot that dies every night in winter? A: No. One jacket relight. Repeated dropouts are spillage or fuel starvation. That is carbon monoxide and unburned gas, not a winter chore.