127
FAULT CODE
Navien
Air Pressure Switch (APS) Issue
High Severity
Engineer Required
The air pressure switch is not operating correctly — it is not confirming adequate airflow before ignition. Reset and check for flue obstructions.
Cold Weather Note
Check flue terminal for ice or debris blockage in cold weather.
Step-by-Step Fix Guide
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Step 1
Check the flue terminal for obstructions
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Step 2
Reset the boiler
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Step 3 Engineer only
If 127 persists, call a Gas Safe engineer to test the APS and fan system
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.