Fault Finding And Resolution; Fault Table - Bosch Worcester Greenstar Comfort II RF Installation And Operating Instructions Manual

Fault finding and resolution

7 Fault finding and resolution
If a fault code is displayed the user must first press the knob to return to the main display.
The last 5 control faults can be viewed in the Faults history (refer to 5.2.4 Maintenance).
If a fault appears that is not listed within the table it could be that a boiler fault has occurred.
The boilers Installation & servicing manual should then be consulted.
7.1

Fault table

Fault
code Problem
The temperature
displayed on the
thermostat unit is
different than the room
temperature
The required room
temperature has not
been achieved
The room temperature is
higher than the set value
No flame symbol visible
on the Room thermostat
Cannot select DHW mode
on the Room thermostat.
NA is displayed.
A21/ Loss of RF signal
A22
A23 Room stat internal sensor
failure
A24 Remote RF unit has a
fault
16
Description
Temperature offset setting is other than 0 Check the temperature offset setting on the
Room to room temperature difference
Airlock
Low system pressure
Time program / weather change
Flow temperature
Thermostat valve in reference room
The Room thermostat is subject to
draught or energy loss
The actual temperature is close to the
target temperature. The control turns the
boiler off early to prevent overshoot.
The flame symbol is not available with oil fired boiler controls.
The Room thermostat is part of a multiple
heating zone system in combination with
the Greenstar Wiring Centre. Only the
primary Room thermostat (the first to be
paired with the Receiver) is controlling
the DHW mode.
The Room thermostat unit is incorrectly
positioned
Receiver or Room thermostat unit has no
power supply
A21 will be displayed at initial
switch on until the two units have
established an RF communication link
Internal room temperature sensor out of
valid range
Another room thermostat in the system
has a problem
Resolution
Programmable thermostat (Setting menu 
Format  Sensor calib. refer to section 5.1.5)
and adjust as required.
Consider differences between rooms due to
draughts, sunshine etc. Move Room thermostat to
a more suitable location if necessary.
Bleed the radiators and vent the heating system.
Top up the system pressure via the filling link.
Is the heating on for long enough.
Set a higher flow temperature.
Operate the TRV to ensure that it does not stick
Fully open the TRV.
Move the Room thermostat to a more suitable
location (refer to section 3.2).
Set the target temperature is at least 2 ºC above
the current displayed temperature. It takes up to 6
minutes for the flame to come on.
Select the required DHW mode on the primary
Room thermostat.
Check signal strength and reposition
Room thermostat for better signal.
Wire the Receiver to a wall plate if the boiler is in a
loft or garage.
Check that boiler has power and that Room
thermostat batteries are not running low (see
Blank display or low battery symbol).
Allow up to 1 minute after power up for the units to
communicate.
Replace RF Room thermostat.
Check other room thermostats within the system
for fault codes.
Comfort II– 6720810965 (2017/02)