Heater displays F19; unit may lock out after several failed ignition attempts.

Safety first: Turn off gas and power before servicing. Do not repeatedly reset a heater that fails to ignite; unburned gas can accumulate.

• Review ignition sequence: Observe one ignition attempt through the sight glass. Note whether the igniter glows/sparks, gas is heard, and flame appears.
• Service ignition components: Clean or replace the igniter and flame sensor as needed. Ensure proper gap and positioning per Thermeau specifications.
• Clean burners: Remove and clean the burner tray to ensure even gas distribution and reliable lighting.
• Check gas supply: Have a gas technician verify inlet and manifold pressures and correct any supply issues.
• Reset lockout: After correcting issues, reset the heater according to the manual. If F19 returns, further professional diagnosis of the gas valve and control board is recommended.