Boiler shows F.33, fan runs but boiler does not ignite

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Blocked flue or air intake, Faulty air pressure sensor or switch, Split or blocked pressure tubing, Incorrect flue installation

Safety: This fault relates to safe removal of combustion products. Do not bypass any safety switches.

Check flue terminal: From outside, ensure the flue outlet and air intake are not blocked by debris, nests, or snow.
Reset boiler: Attempt a reset. If F.33 persists, switch off and call an engineer.
Engineer checks: A professional will inspect the air pressure sensor, tubing, and flue for blockages or incorrect slope, and verify correct operation with a manometer.

Professional Required 5/5

Air Pressure Sensor

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