M.202 on a Vaillant aroTHERM plus: Sensor fault: System temperature

What it means

The manual says: Sensor fault: System temperature.

Part involved: System temperature.

Likely causes:

• System temperature sensor defective.

Is it safe?

The heat pump keeps running.

Resetting itself: yes - message clears when the condition is resolved (maintenance message reset by engineer via Installer level > Resets).

Manual reset: engineer resets maintenance message after work.

What you can check

• Note the full code and text shown on the display (and the date/time it appeared). The operating instructions allow the reset button on the indoor unit (or a reset via the system control) to be pressed once; if the code returns, do not keep resetting - contact your installer or Vaillant.

What the engineer will check

• Check the plug contact on the PCB and on the wiring harness; check that the sensor is working correctly and, if required, replace the sensor.

Who to ask for: Vaillant-trained heat pump installer/engineer (MCS-certified installer).

Certification: MCS installer certification; Vaillant product training recommended.

What you might notice

• No heating
• No hot water

What owners and engineers report

13 owner and engineer reports mention this.

• No heating on the aroTHERM plus (VWL ../6 A): 8 reports
• No hot water on the aroTHERM plus (VWL ../6 A): 5 reports

Sources

• Heat pump control interface module (VWZ AI) operating and installation instructions ↗ · 0020291573_01 · page VWZ AI appliance interface 0020291573_01 p.33; uniTOWER VIH QW 190/6 E 0020291525_05 p.59; VWZ MEH 97/6 hydraulic station 0020291544_03 p.51; aroTHERM split hydraulic station VWL ../5 IS 0020257319_05 p.56 · Reviewed 23 September 2026

A code explains what the controller detected, not a confirmed root cause.

Reviewed: 23 September 2026