Viessmann Vitodens 100 Installation And Service Instructions Manual page 58

Troubleshooting
Fault finding
Note
It is the law that any service work must be carried out by a competent CORGI
registered engineer.
General
Before looking for a fault condition,
check that:
&
The mains electrical supply is
turned on.
&
The clock and / or room thermostat
(if fitted) are calling for heat (CH
'faults' only).
&
The gas service cock is open.
&
The CH isolation cocks are open.
& The system is at design pressure.
Function sequence and possible faults
Control unit is-
sues heat de-
mand
Yes
Fan starts
Yes
Air pressure lim-
iter enables start
(contact closed
between term-
inals "X8.7" and
"X8.8")
58
Display screen
No
after approx. 51 s
No
Fault
F5/F9
No after approx. 51 s
Fault
F5/F9
Before attempting any electrical fault
finding, always conduct the prelimin-
ary electrical system safety checks.
On completion of any service or fault
finding operation involving making or
breaking electrical connections
always check for earth continuity,
polarity and resistance to earth.
Remedy
Increase set value
and ensure heat is
drawn off
Checking fan
cables and plugs
Check fan cables
and fan plug-in
connections,
check fan