F.33
FAULT CODE
Glow-worm
Air Pressure Switch Fault (Energy Range)
High Severity
Engineer Required
On Glow-worm Energy boilers, F.33 indicates an air pressure switch fault — the switch is not confirming correct fan operation before ignition is allowed.
Step-by-Step Fix Guide
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Step 1
Turn off the boiler
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Step 2 Engineer only
Call a Gas Safe engineer to test the air pressure switch, fan, and connecting pipework
Gas Safe Reminder
Work on gas appliances must be carried out by a Gas Safe registered engineer. The steps above cover safe checks a homeowner can perform - any internal component replacement requires a qualified professional. If in doubt, always call an engineer.