Heat pumps · Error codes · IVT
LPIVT · Greenline HT Plus
LP on an IVT Greenline HT Plus: Low pressure switch (LP) tripped
Short answer
On an IVT heat pump, LP means: Low pressure switch (LP) 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: Low pressure switch (LP) tripped.
Part involved: low pressure switch.
Likely causes:
- Air in the heat transfer (brine) system; particle filter on the cold side clogged; lack of refrigerant; HTF pump stopped or set too low a speed; ice in heat exchanger due to lack of antifreeze; faulty expansion valve (alarm every 3-4 weeks).
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
- Check brine expansion vessel/level and top up; bleed brine circuit; clean cold-side particle filter; check sight glass for continuous bubbling (low charge); check HTF pump speed; check antifreeze; check expansion valve.
Who to ask for: heat pump engineer.
Certification: F-Gas category I certificate (refrigerant circuit work).
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.35 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026