F.56
FAULT CODE
Vaillant
Mass Flow Sensor Regulation Fault
High Severity
Engineer Required
The gas valve or its cable harness is defective, causing the mass flow sensor to give incorrect readings for the air/gas mixture.
Step-by-Step Fix Guide
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Step 1
A Gas Safe engineer must inspect the gas valve and its wiring
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Step 2
The gas valve coils may have shorted to earth
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Step 3 Engineer only
Replacement of the gas valve or cable harness may be needed
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.