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Heat pumps · Error codes · IVT
MB1IVT · Greenline HT Plus

MB1 on an IVT Greenline HT Plus: Motor cut-out compressor (MB1): the compressor motor cut-out has tripped

Short answer

On an IVT heat pump, MB1 means: Motor cut-out compressor (MB1): the compressor motor cut-out has tripped. The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause.

Reviewed 23 September 2026 · 1 source

What it means

The manual says: Motor cut-out compressor (MB1): the compressor motor cut-out has tripped.

Part involved: compressor motor cut-out MB1.

Likely causes:

  • Intermittent fault or overload on the power supply; current setting on the motor cut-out too low (compressor current varies summer/winter); contactor or cut-out faulty or loose connections to compressor; compressor error.

Is it safe?

Does the heat pump stop?Yes
SeverityFault — needs a manual reset once the cause is fixed
Engineer needed?Yes

The heat pump stops until the fault clears or is reset.

Manual reset: Ackn. button on Rego 637 control panel.

What you can check

  • Press the Ackn. button on the control panel once (the manual says there is no risk in resetting an alarm; the heat pump restarts within 15 minutes if heat is needed). If the alarm returns, contact your installer. Check the heat pump's breaker/isolator at the consumer unit is on and has not tripped.

What the engineer will check

  • Reset motor cut-out (fuse 1 reset switch on the unit - the user guide lets the householder press it; we list it here per project safety policy); check cut-out current setting; check contactor and compressor connections; test compressor.

Who to ask for: heat pump engineer.

Certification: Qualified electrician / heat pump engineer (electrical fault-finding).

What you might notice

Sources

A code explains what the controller detected, not a confirmed root cause.

Reviewed: 23 September 2026