F84
FAULT CODE
Glow-worm
Flow / Return Sensors Transposed
High Severity
Engineer Required
The flow and return temperature sensors appear to be reading inverted values. Usually a post-service issue.
Step-by-Step Fix Guide
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Step 1
This usually only occurs after service work
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Step 2 Engineer only
The engineer who last worked on the boiler should check the NTC sensor positions
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.