Buderus 800-24 Installation And Servicing Instructions page 41

Code Meaning
4Y
Flow sensor interrupted
Possible
cause
1 Flow sensor faulty or disconnected
2 A short or bad connection in the cable harness
Code Meaning
5C
Boiler shut down after connection with Service Tool
Possible
cause
1 Service tool connection
2 A short or bad connection in the cable harness
3 UBA might be faulty
Code Meaning
6A
F1 fuse defective, or no ionisation message after ignition
Possible
cause
1 There is no flame, ionisation electrode doesn't
glow, fan is turning
2 There is no flame, ionisation electrode does
glow, fan isn't turning
3 There is no flame, ionisation electrode and fan
are working
4 There is a flame, but the flame disappears
when the fan starts up
Subject to modifications resulting from technical improvements !
Installation and servicing instructions condensing gas boiler 800 - 24/29/43/60 and 800 - 24T25/29T25 H/V • edition 02/2006
Action
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)
Check the cable harness and/or connector of the sensor
(see subsection 5.3.12)
Action
Press reset. If fault code remains than try to temporarily
connect a different UBA (see subsection 5.3.5)
Check the cable harness and/or connector of the sensor
(see subsection 5.3.12)
Check the UBA by temporarily connecting an other UBA
(see subsection 5.3.5)
Action
– 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
– Check the fan and KIM connectors and the UBA fuses
– 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
– 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)
Servicing 5
Buderus • http://buderus-domestic.co.uk
41