Tank water heaters
Test gas and electric separately. If one works, the tank and plumbing are fine and you've cut the problem in half.
The short version
- Make sure the tank is full first. Open a hot tap until it runs steady. Electric on a dry tank burns the element out.
- Check the bypass valves are in normal, not winterize.
- Electric: 120V at the element with it switched on? Then check element ohms with power off.
- Gas: listen for the click, spark and whoosh. No spark, no gas, or flame drops out each point somewhere different.
On the job
- Confirm the tank is full: open a hot tap until it runs steady. Check the bypass valves are set for normal use.
- Gas: switch on, watch the fault light. Instant fault = ECO/thermostat open or no 12V. Spark no flame = gas side. Lights then faults = flame sense.
- Meter across the thermostat and ECO on a cold tank: near 0 Ω each. The ECO is about 180°F, the thermostat about 140°F.
- Electric: 120 VAC at the element terminals, then power off and ohm the element: about 10 Ω for 1440 W. Clamp about 12 A on the first run.
- Relief valve drip while heating is thermal expansion: heater off, supply off, open a hot tap, lift the lever until water stops, close the tap.
Numbers
- 1440W element: ~10Ω
- Element bad: OL / open, or reads to the tank
- Element 1440 W: about 10 Ω, about 12 A
- ECO / thermostat: about 180°F / about 140°F
- Supply pressure: under 60 psi or the relief valve weeps
Shop tip
Suburban tanks have an anode rod. Atwood aluminum tanks don't. Don't go looking for one.
Try it on a service call
Put the lesson to work on a hands-on troubleshooting case.