LOW-PRESSURE on a Heliotherm Basic Comfort air split: Evaporation pressure below safety-chain limit
Short answer
On a Heliotherm heat pump, LOW-PRESSURE means: Evaporation pressure below safety-chain limit. 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: Evaporation pressure below safety-chain limit.
Part involved: Low pressure (evaporating pressure).
Likely causes:
- Defective fan.
- Refrigerant deficiency/leak.
- Moisture in circuit - expansion valve frozen.
- Rotalock valve fully opened during commissioning.
- Foreign gas in refrigerant circuit.
Is it safe?
Switch the heat pump off at its isolator and call an engineer.
| 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: Fault clearance function in the controller main menu (web control 321 manual p.27, intended for the Heliotherm competence partner).
What you can check
- Note the error text shown on the controller and contact your Heliotherm competence partner (manual: the heat pump should be shut off and checked by a trained specialist).
- Check the outdoor evaporator is not blocked by leaves, snow or debris.
What the engineer will check
- Inspect outdoor evaporator wiring.
- Leak-test and recharge per chapter 13.
- Check sight glass for moisture.
- Close Rotalock valve.
- Replace refrigerant if contaminated.
Who to ask for: heat pump / refrigeration (Heliotherm competence partner).
Certification: F-gas certification for refrigerant work.
What you might notice
Sources
- Heliotherm Installation Instructions Air Split Heat Pump Basic Comfort Series (Version 1.0, 28.03.2019) - via ManualsLib 3389544 ↗ · Version 1.0 · page 35 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026