70 on a Viessmann Vitotronic 200: Short circuit/lead break, secondary circuit flow temperature sensor downstream of instantaneous heating water heater
Short answer
On a Viessmann heat pump, 70 means: Short circuit/lead break, secondary circuit flow temperature sensor downstream of instantaneous heating water heater. The heat pump stops until the fault clears or is reset. 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, secondary circuit flow temperature sensor downstream of instantaneous heating water heater.
- Room temp. sensor HC1: No frost protection mode via room temperature sensor; No room temperature hook-up; No room temperature-dependent control.
Part involved: Short circuit/lead break, secondary circuit flow temperature sensor downstream of instantaneous heating …; Room temp. sensor HC1.
When it shows: Type "Fault" (S) - triggers "05 Refrigerant circuit" on the heat pump control unit. Heat pump characteristics: Compressor OFF No frost protection mode via room temperature sensor; No room temperature hook-up; No room temperature-dependent control.
Likely causes:
- Short circuit/lead break, secondary circuit flow temperature sensor downstream of instantaneous heating water heater.
- Short circuit, room temperature sensor, heating circuit without mixer A1/HC1.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
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.
- Check the room thermostat/remote control and time-program settings are as expected.
What the engineer will check
- Check resistance value (NTC 10 k Ω) at connection J21 (T2) of the EEV PCB: See "EEV PCB [4-6] / [4-7] ".
- Check remote control. Replace remote control if required: See "Vitotrol" installation and service instructions.
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 176, 95 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026