175
A.12 Battery in the HPMU electronics module
A.12
System characteristics
Incorrect time
Cause
Battery in HPMU electronics module flat.
Measures
1. Replace CR2032 battery in HPMU electronics mod-
ule.
2. Set the time on the programming unit:
Operating instructions
A.16 Minimum flow rate undershot
A.16
System characteristics
■
Refrigerant circuit off: Inverter and compressor can-
not be switched on.
■
Instantaneous heating water heater is switched off.
The instantaneous heating water heater will not start.
Cause
Minimum flow rate undershot
Measures
1. Check secondary pump/heating circuit pump, heat-
ing/cooling circuit 1.
2. Check flow sensor.
A.17 Increased DHW hygiene
A.17
System characteristics
No increased DHW hygiene
Cause
■
Temperature for increased DHW hygiene is not
reached.
■
DHW cylinder volume may be too large
Measures
1. Set period for increased DHW hygiene to fall on a
period with low DHW demand.
2. Check DHW cylinder sizing.
A.19 Temperature limiter has responded
A.19
System characteristics
Heat pump temporarily off
Cause
Temperature limiter has responded.
Measures
1. No action required
2. If the message appears often: Inform Viessmann
Technical Service.
A.21 Hydraulic system pressure
A.21
System characteristics
The safety valve in the indoor unit has opened.
Cause
Hydraulic system pressure too high
Messages
Warning messages (cont.)
6218234
Diagnosis
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