Viessmann Vitotronic 100 GC1 Series Operating Instructions And User's Information Manual page 14

Troubleshooting guide
Diagnosis and correction with single-boiler systems
Fault
Burner does not start; red fault
indicator (see page 5) flashes on the
control unit and red fault lamp is
illuminated on the burner
The rooms are cold even though the
burner is operating
The room temperature is not high
enough with a low outdoor
temperature
The rooms are cold during the day,
but warm at night
Fault symbol "U" appears in the
display window with flashing fault
code
14
Cause
Faulty start of burner
Heating program "w" or "9" is set
(corresponding button is illuminated)
Operation with domestic hot water
tank only:
Domestic hot water supply has
priority
Control unit incorrectly programmed
or set
Control unit incorrectly programmed
or set
Fault on heating system
(continued)
Remedy
Make a new attempt to start by
pressing the reset button
H on the front of the burner hood
with pressure jet burners,
H on the front panel of the boiler
with atmospheric burners.
If the burner still fails to operate
after pressing the reset button,
check the points stated in the
section headed "Starting up the
heating system" and then press the
reset button again.
If the burner still fails to switch on,
contact your heating contractor.
Set heating program "rw"
(page 6)
Wait until the domestic hot water
tank has heated up
Check and, if necessary, correct the
settings for temperatures (page 9)
and the heating program (page 6)
Check and, if necessary, correct the
settings for temperatures (page 9)
and the heating program (page 6)
Make a note of the fault code
(page 12) and inform your heating
contractor