Buderus 800 - Page 43

Servicing 5
Wall-mounted condensing gas boiler Buderus 800 - Subject to modifications resulting from technical improvements!
43
Code Meaning
4Y Flow sensor interrupted
Possible
cause
Action
1 Flow sensor faulty or disconnected Check the sensor and measure if resistance over the
sensor is correct. If not replace safety sensor
(see subsection 5.3.9 and subsection 5.3.10)
2 A short or bad connection in the cable harness Check the cable harness and/or connector of the sensor
(see subsection 5.3.12)
Code Meaning
5C Boiler shut down after connection with Service Tool
Possible
cause
Action
1 Service tool connection Press reset. If fault code remains than try to temporarily
connect a different UBA (see subsection 5.3.5)
2 A short or bad connection in the cable harness Check the cable harness and/or connector of the sensor
(see subsection 5.3.12)
3 UBA might be faulty Check the UBA by temporarily connecting an other UBA
(see subsection 5.3.5)
Code Meaning
6A F1 fuse defective, or no ionisation message after ignition
Possible
cause
Action
1 There is no flame, ionisation electrode doesn’t
glow, fan is turning
– Check wiring of the hot surface ignitor, measure the resistance
of the hot surface ignitor (should be between 50 and 300 Ohm).
Replace hot surface ignitor if necessary (see subsection 5.3.15
and subsection 5.3.16)
– Check the UBA’s F1 fuse, replace if necessary
2 There is no flame, ionisation electrode does
glow, fan isn’t turning
– Check the fan and KIM connectors and the UBA fuses
3 There is no flame, ionisation electrode and fan
are working
– Check and adjust the gas/air ratio (see subsection 2.2.4)
– Check for 24 V~ on the gas valve during start up
– Check the gas-supply pressure (see subsection 2.2.3), this
should be higher than 20 mbar for natural gas.
– Check the earthing cable connections (yellow/green wire)
– Check the cabling on the ionisation electrode
4 There is a flame, but the flame disappears
when the fan starts up
– Check the gas-supply pressure (see subsection 2.2.3), this
should be higher than 20 mbar for natural gas
– Check and adjust the gas/air ratio (see subsection 2.2.4)
– Check the earthing cable connections (yellow/green wire)
– Check the cabling on the ionisation electrode
– Press reset. If fault code remains than try to temporarily connect
a different UBA (see subsection 5.3.5)