D3
FAULT CODE
Worcester Bosch
External Thermostat Short Circuit
Medium Severity
Engineer Required
The external thermostat or room controller wiring has a short circuit. The boiler cannot receive a correct signal from the thermostat.
Step-by-Step Fix Guide
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Step 1
Check the thermostat wiring for visible damage or loose connections
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Step 2 Engineer only
A Gas Safe engineer or electrician will need to test and repair the thermostat circuit
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.