return-line-sensor on a Danfoss heat pump: Sensor fault alternatively cable fault. Return line sensor
Short answer
On a Danfoss heat pump, return-line-sensor means: Sensor fault alternatively cable fault. Return line sensor. 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 · 2 sources
What it means
On the DHP-AQ
The manual says: Sensor fault alternatively cable fault. Return line sensor.
Part involved: return line sensor.
Likely causes:
- Sensor or cable fault.
On the DHP-H
The manual says: Return sensor fault. Return temperature = Supply line - 5 is used. Calculated supply temperature limited to maximum 45°C.
Part involved: return line sensor.
Likely causes:
- Sensor fault or cable fault.
Is it safe?
On the DHP-AQ
| 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 the condition clears (inferred).
On the DHP-H
| 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 the condition clears.
What you can check
On the DHP-AQ
- Note the exact alarm text. The manual allows acknowledging by setting operating mode OFF then back once; if the alarm returns, call an engineer.
On the DHP-H
- Note the exact alarm text. The manual allows acknowledging by setting the operating mode to OFF and then back to the previous mode - do this once; if the alarm returns, leave it and call an engineer.
What the engineer will check
On the DHP-AQ
- 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 DHP-H
- Measure sensor + cable resistance vs 22 kOhm NTC table.
Who to ask for: heat pump engineer.
What you might notice
Sources
- Service Instructions DHP-AQ (VMGFJ202) ↗ · VMGFJ202 · page p.10; p.18 · Reviewed 23 September 2026
- Service instructions DHP-A, DHP-A Opti, DHP-AL, DHP-AL Opti, DHP-C, DHP-H, DHP-H Opti, DHP-H Opti Pro, DHP-L, DHP-L Opti, DHP-L Opti Pro (VMGFC302) ↗ · VMGFC302 (© 2010; PDF regenerated 2024-07-10 on assets.danfoss.com) · page printed p.35, p.42 (Table 16); PDF pp.37, 44 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026