Boiler locks out with E03; fan runs but burner does not light

Safety: Turn off power before working on venting or internal components. Do not operate the boiler with venting disconnected.

• Inspect intake and exhaust: Go outside and check the Dettson boiler vent terminals. Remove any snow, leaves, nests, or debris blocking the intake or exhaust. Ensure vent screens are clear.
• Check condensate drain: For condensing Dettson boilers, verify the condensate trap and drain line are not clogged or frozen. Clear any blockage and ensure the trap is filled with water.
• Examine pressure switch tubing: With power OFF, remove the front panel and locate the air pressure switch. Inspect the silicone tubes for cracks, kinks, or disconnections. Reattach or replace tubing as needed.
• Test pressure switch (basic): Gently tap the switch body; sometimes a stuck diaphragm will release. Do not blow into the switch. If E03 persists, a technician should test continuity across the switch during fan operation.
• Professional service: If venting and tubing are clear but the code remains, the Dettson air pressure switch or combustion fan may be defective. Have a qualified technician test and replace the faulty component.