High Lockout
E.00 – .05 on Baxi 200 Combi (range)

Your boiler has detected a fault with the sensor that monitors water temperature returning to the unit, meaning it cannot operate safely or efficiently.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description

Return temperature sensor short-circuit. Sensor not connected or badly connected.

What causes this fault?

This fault occurs when the boiler's internal computer loses the ability to read the temperature of the water coming back from your radiators. The most common reason is that the sensor itself has suffered a mechanical failure or the electrical wiring connecting it to the main control board has come loose or become damaged.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

Find a Gas Safe engineer
Search the official register →

Related guides you might find useful

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 →

When to replace your boiler

7 signs repair isn't worth it anymore.

Read →