Safety: Turn off power and shut off the gas supply. Working on gas valves should be done with extreme caution.

Inspect wiring: Remove the front panel and locate the Gas Valve Assembly. Check the harness from the ignition control board to the gas valve for loose or burned connectors. Reseat all plugs.
Check control fuses: Some SunHeater models have a small fuse on the main control board. With power off, visually inspect and test the fuse with a multimeter. Replace only with the exact same rating if blown.
Measure gas valve coil resistance: Disconnect the gas valve leads and measure coil resistance. Compare to the service manual specification. An open or shorted coil indicates a bad gas valve that must be replaced.
Verify correct polarity: Ensure line and neutral are correctly wired to the heater. Reversed polarity can cause gas valve errors on some electronic controls.
Test after checks: Restore power and gas, then call for heat. If E09 persists and the valve coil tests good, the ignition control board is likely defective and should be replaced by a professional.

Warning: Do not attempt to disassemble or repair the gas valve itself. Replace the entire assembly if faulty.

Heater displays E09 and locks out; no ignition attempt is heard

Possible Causes