Fault 03 / 20 Medium

Worcester Bosch Fault 03 / 20 Fault Code

Also written as FAULT0320 — same fault.

The Worcester Bosch Fault 03 / 20 fault code means: your boiler is having trouble communicating with the temperature thermostat built into its control panel, which means it doesn't know how warm your home is.. It appears on 1 Worcester Bosch model in our database.

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description: Room temp sensor faulty: There is a circuit break on the room temperature sensor built into the FW 100.

What causes the Worcester Bosch Fault 03 / 20 fault?

This fault occurs when the electrical connection between the boiler's main control board and its built-in digital thermostat is interrupted. The most common reason is a physical breakage in the internal wiring or a component failure within the controller itself, which prevents the boiler from receiving the temperature data it needs to operate.

Typical repair cost £120-£250 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Worcester Bosch models that show the Fault 03 / 20 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Worcester Bosch Fault 03 / 20 fault code information on this page is sourced and cross-checked against the official Worcester Bosch service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026