Buderus Logamax plus GB142-24 Servicing Instructions page 63

Locking boiler fault code 4U
4 U 2 2 2
C U 2 4 0
Press the "Reset" button.
New fault message
4 U or
Check the wire to the supply or return sensor
for signs of short circuiting (page 92).
Is the wire okay?
Check the supply and return sensor
(page 89).
Are the supply and return
sensors okay?
44
page 83
Logamax plus GB142-24/30/45/60 - We reserve the right to make any changes due to technical modifications!
The supply sensor contact is shorted.
The return sensor contact is shorted.
No
C U
?
Yes
No
Yes
No
Yes
Locking boiler-fault code.
Locking boiler-fault code.
Replace the cable loom or the affected part
thereof.
Replace the supply and return sensor
(page 91).
Diagnosis
8
page 31
7
63