Viessmann VITODENS 242-F Installation And Service Instructions Manual page 128

Troubleshooting
Fault codes
(cont.)
Displayed System characteris-
fault code tics
A4 Control mode
A7 Control mode as per
delivered condition
A8 Burner blocked The
venting program is
started automatically
(see page 85)
A9 If a heating circuit
with mixer is connec-
ted, the burner oper-
ates at its lower heat-
ing output.
If only one heating
circuit without mixer
is connected, the
burner is blocked.
b0 Burner blocked
b1 Control mode as per
delivered condition
b4 Controls as if the out-
side temperature
were 0 °C
b5 Control mode as per
delivered condition
b7 Burner blocked
128
Cause
Max. system pres-
sure exceeded
Programming unit
faulty
Air lock in the inter-
nal circulation
pump or minimum
flow rate not ach-
ieved
Internal circulation
pump blocked
Short circuit, flue
gas temperature
sensor
Communication er-
ror, programming
unit
Internal fault
Internal fault
Boiler coding card
faulty
Measures
Check system pressure.
Check the function and
sizing of the expansion
vessel.
Vent the heating system.
Coding address "0E" is
set to "1" to document the
fault. Must be manually
reset to "0" after trouble-
shooting.
Replace programming
unit
Vent the system if the fault
message continues to be
displayed
Check the circulation
pump
Check flue gas tempera-
ture sensor
Check connections and
replace programming unit
if required
Replace the control unit
Replace the control unit
Plug in or replace boiler
coding card