Water heater gas side
Tank water heaters with direct spark ignition fail like furnaces: no spark, no gas, or no flame sensing.
The short version
- Check 12V at the board while it tries to light, and the fuse.
- Watch for spark at the electrode. No spark points to the board, electrode or wiring.
- Spark but no flame: check gas supply, the gas valve and the burner tube for blockage.
- Lights then goes out: flame sensing, a weak flame, or a loose ground.
Numbers
- Electrode gap: about 1/8 in
- Burner to board ground: under 1 Ω
Try it on a service call
Put the lesson to work on a hands-on troubleshooting case.