Medium Lockout
Fault 03 / 20 on Worcester Bosch Greenstar CDi Compact

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.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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 this 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.

Engineer required

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

Find a Gas Safe engineer
Search the official register →

Related fault codes

203View →

Related guides you might find useful

Boiler won't turn on — 9-step checklist

Work through these before the call-out.

Read →

Boiler keeps cutting out

Lockout fault with a reset-needed pattern.

Read →

Yellow or orange flame — CO safety

Safety-critical — turn off, read this.

Read →