01 on a Viessmann Vitotronic 200: Short circuit/lead break, air intake temperature sensor
Short answer
On a Viessmann heat pump, 01 means: Short circuit/lead break, air intake temperature sensor. The heat pump keeps running with some functions stopped. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 2 sources
What it means
The manuals for this range word it in different ways:
- Short circuit/lead break, air intake temperature sensor.
- Short circuit/lead break, primary circuit flow temperature sensor (heat pump air intake).
- Short circuit/lead break, primary circuit flow temperature sensor (heat pump brine inlet).
- Short circuit/lead break, air intake temperature sensor, evaporator (outdoor).
- System fault.
Part involved: Short circuit/lead break, air intake temperature sensor; Short circuit/lead break, primary circuit flow temperature sensor (heat pump air intake); Short circuit/lead break, primary circuit flow temperature sensor (heat pump brine inlet); Short circuit/lead break, air intake temperature sensor, evaporator (outdoor); System fault.
When it shows: Type "Fault" (S) - triggers "05 Refrigerant circuit" on the heat pump control unit. Heat pump characteristics: Operation with temperature value of return temperature sensor in primary circuit, plus 3 K Type "Fault" (S) - triggers "05 Refrigerant circuit" on the heat pump control unit. Heat pump characteristics: Compressor OFF.
Likely causes:
- Short circuit/lead break, air intake temperature sensor.
- Short circuit/lead break, primary circuit flow temperature sensor (heat pump air intake).
- Short circuit/lead break, primary circuit flow temperature sensor (heat pump brine inlet).
- Short circuit/lead break, air intake temperature sensor, evaporator (outdoor).
- Control unit processor faulty.
Is it safe?
| Does the heat pump stop? | Partly |
|---|---|
| Engineer needed? | Yes |
The heat pump keeps running with some functions stopped.
Resetting itself: Not stated in 6150133.
Manual reset: Refrigerant circuit messages cannot be acknowledged in the message history (6150133 p.155); acknowledge the resulting 05/07/A9 message on the control unit.
What you can check
- This code is only visible to engineers in the service menu (Diagnosis > Refrigerant circuit > Message history); homeowners see message 05, 07 or A9 - note that code and call your contractor.
- Note the 2-character message code and message text shown on the Vitotronic 200 display (press OK for details) and give them to your heating contractor (operating instructions 5817913 p.56).
- You may acknowledge the message once with OK as described in the Vitotronic 200 operating instructions; if it reappears, do not keep acknowledging it - call your contractor.
What the engineer will check
- Check resistance value (Pt500A) at the sensor connection of the EEV PCB: See "EEV PCB [2] ".
- Check resistance value (NTC 10 k) Ω at connection J13 (T5) of the EEV PCB: See "EEV PCB [4-3] / [4-4] ".
- Check resistance value (NTC 10 k) Ω at connection J13 (T5) of the EEV PCB: See "EEV PCB [4-6] / [4-7] ".
- Check resistance value (NTC 15 k) Ω at connection T-SENSOR2 on the main PCB: See "Main PCB [7] / [7-1] ".
- Replace controller and sensor PCB.
Who to ask for: Viessmann-trained heat pump engineer with F-gas refrigeration certification; Viessmann-trained heat pump installer/service engineer.
Certification: F-gas certificate (UK F-gas Regulations; Viessmann: refrigerant work by authorised refrigeration engineers only).
What you might notice
Sources
- Service instructions Vitotronic 200 type WO1C heat pump control unit (air/water split & monobloc, brine/water) (6150133, 2023-07) ↗ · 6150133 VSA00004 · pages 156, 166, 173, 183 · Reviewed 23 September 2026
- Service instructions Vitotronic 200 WO1C (5790974 GB, 2023-09) – brine/water & split variants ↗ · 5790974 VSA00002 · page 61 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026