Viessmann Vitocal 300-G Installation And Service Instructions Manual page 126

Troubleshooting
Control unit diagnostics
ID Message
(priority)
A9 Heat pump
("U")
EXT Electric heat-
ing ("U")
AD Mixer heating
DHW ("U")
AE DHW sens. in-
terchanged
("i")
126
(cont.)
1. Cause
2. Measures
1. Safety high pressure, control high
pressure 10 times in sequence/ 24 h
period, fault refrigerant circuit con-
trol, all primary/secondary tempera-
ture sensors faulty, low pressure
response 10 times in sequence
2. Message history: Scan further mes-
sages (page 119), check flow rates,
check motor currents/motor protec-
tion switch, check safety high pres-
sure limiter
Note
Switch appliance off and on after
removing the cause for the message.
Danger
Touching 'live' components in
the working area can result in
the transfer of dangerous body
currents.
Ensure the device is at zero
volts before carrying out the
instantaneous heating water
heater or prior to resetting the
high limit safety cut-out.
1. Instantaneous heating water heater
faulty or high limit safety cut-out has
responded
2. Check the instantaneous heating
water heater and the high limit safety
cut-out and reset, if required.
heater installation instructions)
1. Three-way valve faulty
2. Check the three-way valve and
replace, if required
1. DHW top/bottom interchanged. The
control unit interchanges the sen-
sors internally.
2. No measures required
Access
right
Customer
Customer
Customer
Heating en-
gineer