COMPRESSOR-ERROR on a Heliotherm Basic Comfort air split: High/low pressure difference falls below 3.5 bar
Short answer
On a Heliotherm heat pump, COMPRESSOR-ERROR means: High/low pressure difference falls below 3.5 bar. 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: High/low pressure difference falls below 3.5 bar.
Part involved: Compressor error.
Likely causes:
- U_Block not connected - compressor not running.
- Wrong compressor rotation direction.
- No power supply to compressor.
- 4-way valve in middle position.
- Energy source to heating water temperature difference too low.
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.
- Check the heating system pressure gauge reading.
What the engineer will check
- Connect U_Block contact.
- Correct rotation direction.
- Check fuses and cables.
- Increase compressor start speed.
- Restrict heating-side mass flow.
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 36 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026