Gas Water Heater Parts: Thermocouples, Gas Valves and Maintenance
Guide to propane and natural gas water heater parts — thermocouple, gas control valve, burner, anode rod and venting. Learn the common failure symptoms and which parts you can replace yourself.
How a Gas Water Heater Works
A gas water heater burns propane or natural gas under the tank to heat the water. The gas control valve regulates the burner, the thermocouple (or electronic sensor) proves the pilot flame, and the thermostat maintains temperature. When parts fail, you get no hot water, lukewarm water, or a pilot that will not stay lit.
Key Gas Water Heater Parts
- Gas control valve: the brain — includes the thermostat, pilot controls and gas shut-off. Fails with age and is the most expensive common part.
- Thermocouple: senses the pilot flame. When it fails, the pilot lights but the valve closes when you release the knob.
- Burner assembly: distributes gas under the tank. Rust and soot reduce efficiency.
- Pilot tube: delivers the small gas flow that keeps the pilot lit. Can clog with dust.
- Anode rod: protects the tank from corrosion. Replace every 3–5 years to extend tank life.
- T&P relief valve: safety valve that releases pressure. Test it yearly.
Common Failure Symptoms
| Symptom | Likely Part |
|---|---|
| Pilot won't stay lit | Thermocouple |
| No hot water, no burner | Gas control valve or thermocouple |
| Lukewarm water | Thermostat setting, sediment, or anode rod |
| Rumbling noise | Sediment buildup at the bottom of the tank |
| Water smells like rotten eggs | Anode rod reacting with water chemistry |
Replacing the Thermocouple
If the pilot lights but goes out when you release the knob, the thermocouple is the usual culprit. Replacement takes about 30 minutes: shut off the gas, remove the access panel, unclip the old thermocouple from the valve, install the new one, and relight the pilot following the label on the tank.
When to Call a Professional
Gas control valve replacement involves working with the gas supply and is best done by a licensed technician. Venting repairs and any work on the gas line also require a professional in most provinces. Tank replacement is a job for an installer — old tanks rust and can fail dangerously.
Propane vs Natural Gas Water Heaters
Water heaters are fuel-specific. Propane units use a smaller orifice and different gas valve configuration than natural gas. If you switch fuels, the conversion kit must match the heater brand and model. Never adapt fittings to use the wrong fuel.