D5
FAULT CODE
Worcester Bosch
Primary Flow Thermistor Fault
Medium Severity
Engineer Required
The main flow temperature sensor is giving an out-of-range reading, preventing the boiler from monitoring water temperature accurately.
Step-by-Step Fix Guide
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Step 1
Reset once
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Step 2 Engineer only
If fault persists, call a Gas Safe engineer to replace the NTC thermistor
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.