Heat pumps · Error codes · IVT
MB2IVT · Greenline HT Plus
MB2 on an IVT Greenline HT Plus: Motor cut-out HTF (heat transfer fluid / brine) pump (MB2) - models C11, E11, E14, E17
Short answer
On an IVT heat pump, MB2 means: Motor cut-out HTF (heat transfer fluid / brine) pump (MB2) - models C11, E11, E14, E17. 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 HTF (heat transfer fluid / brine) pump (MB2) - models C11, E11, E14, E17.
Part involved: brine (HTF) pump motor cut-out MB2.
Likely causes:
- HTF pump blocked by contamination; faulty HTF pump electric motor; temporary error.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — 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. Look at the brine expansion tank: the fluid level should be visible (user guide check). Do not refill or open the ground-loop circuit yourself - call the installer.
What the engineer will check
- Loosen the pump venting screw and clear dirt / free the rotor (user guide describes this as a user action - listed here per safety policy); check pump motor; replace pump.
Who to ask for: heat pump engineer.
What you might notice
Sources
- Greenline HT Plus C and E Guide to installation, commissioning and maintenance (Art. no 290410-29, v1.1) ↗ · 290410-29 v1.1 · page p.34 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026