A strange smell near a water heater may come from the hot water, a nearby drain or the appliance itself. A sulphur smell in hot water can develop in a storage tank, while gas, burning plastic, smoke or sparking around the heater may signal an urgent gas or electrical fault.
If you smell gas near the water heater, do not investigate, use flames, operate electrical switches or use a phone inside. Move everyone outside. Call 000 for immediate danger, then contact your gas distributor’s emergency line from a safe place. The distributor and number vary by address and appear on your gas bill.
For smoke, sparking or a burning or melting-plastic smell, keep away from the heater and switchboard. Call 000 if there is fire or immediate danger, and arrange urgent help from a licensed electrician or appropriately licensed plumber.
What different smells may indicate
- Rotten egg or sulphur smell only in hot water: Hydrogen sulphide may form through bacterial activity or a reaction involving sulphates and a magnesium anode rod in a storage tank, particularly after water has stood unused. See the guide to rotten-egg smells in hot water for the safe next checks.
- Gas-like or rotten egg smell in the air: Treat it as a possible gas leak. Leave immediately without trying to find the source.
- Musty smell around the unit: A leak or condensation may be affecting nearby materials. Observe only from a safe distance. Do not remove covers or disturb suspected mould.
- Metallic smell in the water: Corrosion, metal pipework or water chemistry may be involved. If colour has also changed, check what rusty or brown hot water can indicate.
- Burning, hot-plastic or chemical smell: Wiring, insulation or another component may be overheating. Do not touch or use the heater until a qualified person has assessed it.
Instantaneous heaters do not have a storage tank or tank anode, so tank-related bacterial growth and anode reactions do not apply.
How to locate the smell safely
If there are no signs of gas, smoke, sparking or overheating, compare the hot and cold water at several fixtures:
- Check cold water: Run it into a clean glass. Move away from the basin or floor waste before smelling it, as a drain can create a misleading sulphur odour.
- Compare hot water: Repeat with hot water while avoiding scalding. Do not taste the water or use smell alone to judge whether it is safe.
- Try another fixture: An odour only in hot water points towards the heater or hot-water pipework. An odour in both supplies at several fixtures may involve the incoming supply or property pipework.
- Note the location: Determine whether the smell is in the collected water or the air around the appliance. Do not sniff around the heater, remove covers, open gas components, drain the tank or adjust its temperature.
Arrange a licensed plumber’s assessment if the smell persists, repeatedly returns, appears to come from the heater, or occurs with discoloured water or visible leakage. Other gas hot-water failure signs can help you describe the symptoms without opening or testing the appliance.
For a persistent water-heater smell, contact an appropriately licensed plumber. For suspected gas leakage, leave first and contact emergency services or your gas distributor from outside, then arrange licensed gas leak detection and repair once the immediate danger has been addressed.