PHASE-SEQUENCE on an IVT Greenline HT Plus: Phase sequence fault: one or two phases down, or phase sequence to the heat pump incorrect
Short answer
On an IVT heat pump, PHASE-SEQUENCE means: Phase sequence fault: one or two phases down, or phase sequence to the heat pump incorrect. 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: Phase sequence fault: one or two phases down, or phase sequence to the heat pump incorrect.
Part involved: phase guard.
Likely causes:
- One or two phases down; incorrect phase sequence (only rectifiable by an electrician). If power does not return on all phases at the same time during external electrical work, Rego may give a false phase-sequence alarm.
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
- Check the heat pump's breaker/isolator at the consumer unit is on and has not tripped. 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.
What the engineer will check
- Electrician to swap phase sequence on incoming supply.
Who to ask for: heat pump engineer.
Certification: Qualified electrician / heat pump engineer (electrical fault-finding).
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.37 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026