Viessmann VITOCAL 151-A Installation And Service Instructions Manual page 116

Troubleshooting
Warning messages
Message code System characteristics
A.91 The refrigerant circuit is
■
temporarily switched off
Central heating and DHW
■
heating only via instantane-
ous heating water heater
A.93 Refrigerant circuit operation
impaired
A.94 Refrigerant circuit operation
impaired
A.96 Unusual operating noise
■
Unusual starting and opera-
■
tional characteristics
A.99 Refrigerant circuit temporarily
off (condenser frost protec-
tion)
A.100 Settings on the heat pump
control unit deleted
116
(cont.)
Cause
■
■
■
Values for hot gas pres-
sure in relation to hot gas
temperature not plausible
Values for suction gas
pressure in relation to suc-
tion gas temperature not
plausible
Air in the secondary circuit Vent the system. Top up with water
Flow temperature in sec-
ondary circuit downstream
of condenser too low
Data memory on the elec-
tronics modules faulty
Outside temperature too
low for heat pump oper-
ation
Operation without out-
door unit, for example
for screed drying
Fault refrigerant circuit
Measures
No action required
Check sensors. Replace both sen-
sors if required.
To check the high pressure sen-
■
sor, measure the voltage at con-
nection X14.1 to X14.3 of the
VCMU refrigerant circuit control-
ler (0 to 5 V).
To check the hot gas tempera-
■
ture sensor, check resistance
value (NTC 10 k ) at connec-
Ω
tion X14.9/X14.10 of the
VCMU refrigerant circuit control-
ler.
Check sensors. Replace both sen-
sors if required.
To check the low pressure sen-
■
sor, measure the voltage at con-
nection X14.4 to X14.6 of the
VCMU refrigerant circuit control-
ler (0 to 5 V).
To check the suction gas temper-
■
ature sensor, check resistance
value (NTC 10 k ) at connec-
Ω
tion X14.7/X14.8 of the
VCMU refrigerant circuit control-
ler.
if required.
No action required
No action required
■
If the fault occurs repeatedly, re-
■
place electronics modules.