F25 error, appliance locks out, may be associated with flue gas recirculation or high flue temperature

Safety first: Turn off power and gas. Do not operate the heater until the flue system is checked. Risk of carbon monoxide exposure.

• Inspect flue terminal: Ensure the concentric terminal is clear of obstructions and meets Protherm clearance requirements from walls, windows, and corners.
• Check flue joints: Verify that all flue sections are correctly locked and sealed. Replace any damaged seals or pipes.
• Check air intake: Make sure the air intake is not drawing in flue gases from another appliance or from a poorly positioned terminal.
• Professional flue test: Have a qualified technician perform a flue gas analysis and draft test to confirm safe operation.

Warning: Never modify the flue system without following Protherm installation instructions and local regulations.