Furnace locks out with E02, fan may run briefly, burner does not start.

Safety: Isolate electrical power and close the gas valve before opening the casing. Risk of burns from hot components.

• Check system pressure and circulation: If the furnace is part of a hydronic system, verify that the system pressure is within the range specified on the data plate (typically 1.0–1.5 bar cold). Low pressure or air in the system can cause overheating. Top up via the filling loop if allowed by local regulations.
• Inspect flue and air intake: From outside, ensure the concentric flue terminal is not blocked by leaves, snow, or debris. Inside, visually check that the flue connection to the furnace is secure and not crushed or obstructed.
• Clean condensate trap: Many Chaffoteaux condensing furnaces have a plastic condensate trap at the base of the heat exchanger. Remove the trap (place a container underneath), flush it with clean water, and ensure the condensate pipe is not frozen or blocked.
• Overheat thermostat reset: Locate the manual reset overheat thermostat on the primary heat exchanger (refer to the service manual). If it has a reset button, press it gently until it clicks. If it trips repeatedly, there is an underlying circulation or heat exchanger blockage issue that requires a professional.
• Restart and monitor: Restore power and gas, reset the furnace, and observe operation. If E02 returns, contact a qualified technician to check the primary heat exchanger, pump operation, and safety thermostat wiring.