heat-pressure-error on a Thermia Atec: The expected pressure and temperature change in the refrigerant circuit has not happened in the correct way at compressor start
Short answer
On a Thermia heat pump, heat-pressure-error means: The expected pressure and temperature change in the refrigerant circuit has not happened in the correct way at compressor start. 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: The expected pressure and temperature change in the refrigerant circuit has not happened in the correct way at compressor start.
Part involved: compressor start monitoring.
Likely causes:
- On 3-phase units can indicate incorrect phase sequence (appears about a minute after compressor start); otherwise refrigerant circuit not building pressure/temperature. (causes from the equivalent Danfoss DHP-AQ service instructions VMGFJ202).
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: Set operating mode OFF then back to the desired mode.
What you can check
- Note the exact alarm text. Check the heat pump's breaker/isolator at the consumer unit is on and has not tripped. Acknowledge once (operating mode OFF then back); if it remains, contact a service technician (user manual 086L0130 p.25).
What the engineer will check
- Check discharge pipe gets hot; listen for reverse-running compressor; swap two incoming phases if sequence wrong; otherwise investigate refrigerant circuit.
Who to ask for: heat pump engineer.
Certification: F-Gas category I certificate (refrigerant circuit work).
What you might notice
Sources
- Service Instructions Atec (VIIFM102) - silo.tips copy ↗ · VIIFM102 · page p.10 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026