High Lockout
E151 on Potterton Promax

Your boiler's computer control board has developed a fault and can no longer communicate with the system components, causing the unit to shut down for safety.

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

Printed circuit board (PCB) error

What causes this fault?

This fault occurs when the boiler's internal computer experiences a software crash or a physical component failure on the control board. It is often caused by electrical surges, moisture ingress, or simply the natural degradation of the solder joints and capacitors over time. Because the board can no longer safely monitor the boiler's sensors, it shuts the system down as a precaution.

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 fault codes

E133View →E152View →

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 →