Symptoms
- Faint hissing sound coming from the tank area
- Sound may be more noticeable right after heating
- No obvious puddle of water yet
- Could be near the top or bottom of the tank
Likely causes
- CommonCondensation dripping onto a hot surfaceWater condensing on cold supply lines can drip onto the tank's warm exterior and briefly hiss as it evaporates.
- CommonSmall leak dripping onto the burner assembly (gas units)A minor leak at a fitting above the burner can hiss as drops hit the hot burner cover.
- PossibleMineral deposits or sediment shifting inside the tankMovement of sediment during heating can sometimes create a soft hissing or fizzing sound.
- Less commonGas leak at a fitting (less common but serious)A hiss combined with a rotten-egg gas smell warrants immediate caution.
What to do
- Check immediately for any gas smell along with the hissing; if present, treat it as an emergency.
- Dry the top and surrounding fittings and look for any dripping that could be causing the sound.
- Check nearby cold water pipes for condensation that could be dripping onto the tank.
- If it's a gas unit and you find a small drip landing on the burner area, treat it as a leak needing prompt attention rather than just noise.
- Note whether the hiss coincides specifically with the heating cycle, which points more toward sediment or condensation.
- If you can't identify a clear source, monitor closely over the next day and don't ignore a persistent, unexplained hiss.
Tools and parts
- Flashlight
- Towel
When to call a pro
If you can't find an obvious water source for the hiss, or suspect it could be gas-related, have a plumber or gas technician inspect it before continuing to use the unit.
Safety
Use caution
If the hissing is accompanied by any gas odor, treat it as a possible gas leak: leave the area and call your gas utility or 911 from outside rather than investigating further yourself.