Buderus Logamax plus GB142-24 Servicing Instructions page 59

Locking boiler fault code 4A
The supply sensor has measured a
4 A
2 1 8
temperature higher than 221 °F (105 °C).
The return sensor has measured a
2 8 6
C A
temperature higher than 221 °F (105 °C).
Press the "Reset" button.
New fault message
C A 4
Are all servicing cocks
open?
Is the
system pressure (measured on the
boiler) in the heating system at least
14.5 psi (1 bar)?
Is at least
one thermostatic valve
open?
Check the primary
circulation pump.
Is the primary circulation
pump okay?
Check the supply or 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!
No
A
?
Yes
No
Yes
No
Yes
No
Yes
No
Yes
No
Yes
Locking boiler-fault code.
Locking boiler-fault code.
Open the servicing cocks.
Fill and bleed the heating system.
Open a thermostatic valve.
Replace the primary
circulation pump.
Replace the supply and return sensor
(page 91).
Diagnosis
8
page 31
7
59