outdoor-sensor on a Thermia heat pump: Sensor fault alternatively cable fault
Short answer
On a Thermia heat pump, outdoor-sensor means: Sensor fault alternatively cable fault. The heat pump keeps running with some functions stopped. An engineer is needed to fix the cause. The wording differs by model range — each is shown below.
Reviewed 23 September 2026 · 3 sources
What it means
On the Atec
The manual says: Sensor fault alternatively cable fault.
Part involved: outdoor sensor.
Likely causes:
- Sensor or cable fault. (causes from the equivalent Danfoss DHP-AQ service instructions VMGFJ202).
On the Diplomat
The manual says: Fault in outside sensor. When the control system calculates the heat demand, zero degrees is used.
Part involved: outdoor sensor.
On the iTec
The manual says: Something would likely have happened to the cable connection to the outdoor sensor, the cable itself or the sensor. Check for physical damages.
Part involved: outdoor sensor.
Is it safe?
On the Atec
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
On the Diplomat
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
Resetting itself: Yes, when condition clears (inferred).
On the iTec
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
Manual reset: Set operating mode OFF then back.
What you can check
On the Atec
- Note the exact alarm text. Acknowledge once (operating mode OFF then back); if it remains, contact a service technician (user manual 086L0130 p.25).
On the Diplomat
- Note the exact alarm text. Acknowledge once by setting operating mode OFF then back; 'Other alarm message: reset the alarm; if the alarm remains, contact a service technician' (VUGFD302 p.16).
On the iTec
- Look (without touching electrics) for visible damage to the outdoor sensor or its cable on the outside wall; acknowledge once via operating mode OFF then back; if it remains contact your installer.
What the engineer will check
On the Atec
- Disconnect the sensor and measure resistance with and without its cable against the ohm table in 'Measurement points' (section 3.3); replace the sensor if out of tolerance, otherwise the cable.
Who to ask for: heat pump engineer.
On the Diplomat
- Measure sensor/cable resistance (150 Ohm-type table). Causes per the equivalent Danfoss service instructions VMGFC302 (same Danfoss-era controller) - not stated in the Thermia user manual.
Who to ask for: heat pump engineer.
On the iTec
- Measure sensor and cable resistance; repair cable or replace sensor.
Who to ask for: heat pump engineer.
What you might notice
Sources
- Service Instructions Atec (VIIFM102) - silo.tips copy ↗ · VIIFM102 · page p.10 · Reviewed 23 September 2026
- User manual Atria, Atria Duo, Atria Duo Optimum, Atria Optimum, Comfort, Diplomat, Diplomat Duo, Diplomat Duo Optimum (G2), Diplomat Optimum (G2) - 086U6297 Rev. 6 EN ↗ · 086U6297 Rev. 6 · page printed p.41 (PDF p.43) · Reviewed 23 September 2026
- Thermia iTec User Manual (VUJSI102) - ManualsLib ↗ · VUJSI102 · page p.23 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026