Bosch Thermotechnology MBC 2, Manual

Page: 24 / 28

Faults
MBC 2 – 6 720 810 583 (2014/02) 24
Fault situation
Symptom Diagnosis Remedy
Operating code on
ModuLine
i
RT)
thermostat
Led boiler 1
and/or boiler 2
on MBC 2
External fault reporting
Display
code
Service
code
External fault
contact Fault LED
on MBC 2
4 U
Off after max.
4 minutes Closed, lamp
or bell activat-
ed Flashes rap-
idly, 8 x per
second Supply temperature sensor
has short-circuited. (This
fault has a higher priority than
a boiler fault code.) ▶ Check the connections and the wir-
ing between the supply tempera-
ture sensor and the MBC 2.
▶ Check the supply temperature sen-
sor. See table 5.
4 Y
Off after max.
4 minutes Closed, lamp
or bell activat-
ed Flashes rap-
idly, 8 x per
second Supply temperature sensor is
not connected. (This fault
code has a higher priority
than a boiler fault code) ▶ Check the connections and the wir-
ing between the supply tempera-
ture sensor and the MBC 2.
▶ Check the supply temperature sen-
sor. See table 5.
5 H
Flashes slowly,
1 x per second Closed, lamp
or bell activat-
ed Lit up No communication between
MBC 2 and one boiler or be-
tween MBC 2 and both boil-
ers ▶ Check the connections and the wir-
ing between the 2 boilers and the
MBC 2.
- - - -
Lit up (regardless
of burner status) Opened, lamp
or bell not acti-
vated Off Outside temperature sensor
is not connected to the
MBC 2, or outside tempera-
ture sensor has short-circuit-
ed ▶ Check the connections and the wir-
ing between the outside tempera-
ture sensor and the MBC 2.
▶ Check the outside temperature sen-
sor. See table 4.
The fault code for this
boiler Flashes rapidly,
8 x per second Closed, lamp
or bell activat-
ed Lit up Locking or blocking fault in
one boiler ▶ See installation instructions or the
user manual for the boiler.
The fault of boiler that
failed first Flashes rapidly,
8 x per second Closed, lamp
or bell activat-
ed Lit up Locking or blocking fault in
both boilers ▶ See installation instructions or the
user manual for the boiler.
None or flashing display Off Closed, lamp
or bell possibly
activated Off There is no 230 V power sup-
ply to the MBC 2 ▶ Check the 230 V connection to the
MBC 2, and the power supply ca-
ble.
▶ Check that the electrical wall socket
is supplied with 230 V voltage and
insert the plug.
None or flashing display Off after max.
4 minutes Closed, lamp
or bell activat-
ed Flashes
slowly, 1 x
per second No communication between
MBC 2 and the ModuLine
(
i
RT) thermostat. (Frost pro-
tection remains active, and
hot water operation remains
possible.)
▶ Check the connections between the
ModuLine (
i
RT) thermostat and the
MBC 2.
▶ Check the wiring between the
ModuLine (
i
RT) thermostat and the
MBC 2
▶ Check the ModuLine (
i
RT) thermo-
stat.
No hot water, central heating
remains. ▶ Check if the setting hot water on/off
is set to “on” on the ModuLine (
i
RT)
thermostat.
▶ If a ModuLine (
i
RT) thermostat
without this setting option is
present, check if a ModuLine (
i
RT)
thermostat has been present. If so,
place temporary a ModuLine
thermostat with this setting option,
set the setting hot water on/off to
“on” and place the other thermostat
back.
Table 2 Fault situation