Buderus Logamax plus GB142-24 Servicing Instructions page 61

Locking boiler fault code 4L
The safety sensor is shorted or measures
2 2 0
4 L
temperatures higher than 266 °F (130 °C).
Press the "Reset" button.
New fault message
Are all servicing cocks
open?
Is the pressure 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 wire to the safety sensor for signs
of short circuiting (page 92).
Is the wire okay?
25
page 62
Logamax plus GB142-24/30/45/60 - We reserve the right to make any changes due to technical modifications!
No
4 L
?
Yes
No
Yes
No
Yes
No
Yes
No
Yes
No
Yes
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 cable loom or the affected part
thereof.
Diagnosis
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