High Lockout
E40 on Vokera Condexa Pro

Your boiler has detected an issue with the electrical power supply frequency coming into your home.

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

50 Hz error

What causes this fault?

This fault occurs when the boiler's internal computer detects that the incoming electricity supply is not at the steady 50Hz frequency required for safe operation. The most common reason is an issue with the local power grid or a malfunctioning main control board failing to read the electrical signal correctly. In some cases, it can be triggered by unstable power from an external generator or a faulty uninterruptible power supply (UPS).

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

E41View →E42View →

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 →