Viessmann VITOCAL 151-A Installation And Service Instructions Manual page 122

Indoor unit maintenance
Removing the programming unit and electronics...
3.
1.
5.
Fig. 72
Removing the EHCU electronics module
Danger
Contact with live components can lead to seri-
ous injury from electric current. Some compo-
nents on PCBs remain live even after the power
supply has been switched off.
Never touch electrical terminal areas.
■
■ When working on the indoor or outdoor unit,
isolate the system from the power supply, e.g.
at a separate MCB/fuse or a mains isolator.
Check that it is no longer live. Safeguard
against unauthorised reconnection.
Prior to working on the appliance, wait at
■
least 4 min until the voltage has completely
dropped out.
122
(cont.)
After replacing the HPMU electronics module, repeat
the commissioning procedure: See chapter "Commis-
sioning".
2. 2x
4.
Remove programming unit: See chapter "Removing
the HMI programming unit".
Fold open the HPMU electronics module if required:
See Fig. 72.