Water Heater Pilot Goes Out in Cold Weather
On this page (5 sections)
The Short Answer: When a pilot goes out only in cold or windy weather, the cause is usually air, not the thermocouple: wind blowing down the vent, exhaust fans and a tightly closed house pulling air backward through the draft hood, or condensation dripping onto the pilot. On propane, cold weather lowers tank pressure and can starve the pilot. Relight once per the label, then look for the pattern.
Match the pattern to the cause
| When the pilot goes out | Likely cause |
|---|---|
| On windy days, especially from one direction | Downdraft through the vent or a damaged or missing vent cap |
| When the dryer, range hood, bath fans, or a fireplace are running | Negative pressure in a closed-up house drawing air down the vent |
| After long burner runs on very cold mornings, with drips or rust near the pilot | Condensation forming in a cold flue and dripping down |
| On propane, during cold snaps, with other propane appliances weak too | Low tank pressure from cold or a low fuel level, or a frozen regulator |
| Any day, regardless of weather | Not weather-related; see why a gas water heater won’t stay lit |
Why winter makes it worse
A standard gas water heater relies on warm exhaust rising up the vent. In winter, homes are sealed tight, and exhaust fans and dryers pull air out. If the house cannot draw replacement air from elsewhere, it may pull it down the water heater vent, which disturbs the pilot and can also spill exhaust back into the room. A heater in a closet whose louvered door was replaced, or a utility room that was recently weatherstripped, is a common setup for this.
Propane vaporizes less readily as temperature drops, so tank pressure falls in very cold weather, especially with a small or low tank feeding several appliances. The pilot is the smallest flame in the system and often the first to suffer.
Condensation is heaviest when a cold flue meets a long burner run. Water dripping onto the pilot can put it out; see water dripping on the pilot light.
What you can check safely
- Relight once, following the label on the heater. If it goes out again soon, stop and look for the pattern.
- Turn off exhaust fans and the dryer and see whether the pilot stays lit. If it does, the house needs more combustion air.
- Check the closet or room. Restore louvered doors or vents if they have been blocked, and keep the base of the heater clear of lint and storage.
- Look at the vent cap from outside for damage or a missing cap.
- Check the propane tank level and whether other propane appliances are weak. If so, call your propane supplier.
- Make sure CO alarms are working on the same level as the heater and near bedrooms.
What the technician will check
A technician tests draft at the draft hood with fans and appliances running, checks the vent height, cap, and routing, and assesses combustion-air openings. If the house is too tight, solutions include a dedicated outside-air supply for the space or, in some cases, a different venting arrangement. On propane, they check pressure at the appliance with the system under load, and the supplier checks the regulator. They also confirm the pilot flame and thermocouple are in good condition, since a marginal pilot is the first to fail in a draft.
Frequently Asked Questions
Q: Should I replace the thermocouple if the pilot only goes out in winter? A: Probably not first. A thermocouple that works all summer usually still works. Fix the draft, air supply, or propane issue first; if the pilot then goes out on calm days too, the thermocouple becomes a suspect.
Q: Is it safe to keep relighting the pilot every day? A: No. A pilot that keeps going out from downdraft can indicate exhaust spilling into the home. Have the venting and combustion air checked rather than relighting repeatedly.
Manuals and supporting references
These links distinguish general safety information from model-specific documentation. A manual directory helps you locate your unit’s instructions; it does not establish that every model uses the same parts, codes, or test values.
- PG&E: recognizing and responding to a gas leak (opens in a new tab)Emergency actions for suspected fuel-gas leaks.
- CPSC: carbon monoxide fact sheet (opens in a new tab)Carbon monoxide hazards and emergency response.
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