04 on a Viessmann Vitotronic 200: Short circuit/lead break, hot gas temperature sensor
Short answer
On a Viessmann heat pump, 04 means: Short circuit/lead break, hot gas temperature sensor. The heat pump keeps running. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manuals for this range word it in different ways:
- Short circuit/lead break, hot gas temperature sensor.
- Short circuit/lead break, hot gas temperature sensor, compressor (discharged).
- Elec. heating blocked: The instantaneous heating water heater is not started, not even for frost protection. ! Please note If the compressor does not start, the system may no longer ….
Part involved: Short circuit/lead break, hot gas temperature sensor; Short circuit/lead break, hot gas temperature sensor, compressor (discharged); Elec. heating blocked.
When it shows: Type "Fault" (S) - triggers "05 Refrigerant circuit" on the heat pump control unit. Heat pump characteristics:; Compressor remains in operation.; Energy statement is not calculated correctly: See chapter "Diagnosis, energy statement". Type "Fault" (S) - triggers "05 Refrigerant circuit" on the heat pump control unit. Heat pump characteristics: Compressor OFF Type "Fault" (S) - triggers "05 Refrigerant circuit" on the heat pump control unit. Heat pump characteristics: Both compressors OFF Type "Fault" (S) - triggers "05 Refrigerant circuit" on the heat pump control unit. Heat pump characteristics: Cooling mode:; Compressor remains in operation. Heating mode:; Compressor OFF The instantaneous heating water heater is not started, not even for frost protection. ! Please note If the compressor does not start, the system may no longer be protected against frost. Ensure frost protection on site.
Likely causes:
- Short circuit/lead break, hot gas temperature sensor.
- Short circuit/lead break, hot gas temperature sensor, compressor (discharged).
- The prompt "Secondary circuit filled?" during enabling of the instantaneous heating water heater was answered with "No". "Enable instantaneous heating water heater 7900" is automatically ….
Is it safe?
| Does the heat pump stop? | No |
|---|---|
| Engineer needed? | Yes |
The heat pump keeps running.
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 (T6) of the EEV PCB: See "EEV PCB [4-3] / [4-4] ".
- Check resistance value (NTC 10 k) Ω at connection J13 (T6) of the EEV PCB: See "EEV PCB [4-6] / [4-7] ".
- Check resistance value (NTC 10 k) Ω at sensor connection on the EEV PCB: See "Controller PCB and EEV PCB [6] ".
- Check resistance value (NTC 50 k) Ω at connection T-SENSOR2 on the main PCB: See "Main PCB [7] / [7-1] ".
- Fill and vent the secondary circuit. Then enable the instantaneous heating water heater: Set "Enable instantaneous heating water heater 7900" to "1". Confirm prompt "Secondary ….
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, 167, 173, 180, 183, 85 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026