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2/f/

Locking fault 2/f/ (2/6/0) - No temperature increase after burner ignition

Buderus · Logamax plus Boilers

What does 2/f/ mean?

After the burner starts, the flow temperature sensor has not detected any increase in the heating system's water temperature. This indicates a problem with heat transfer. As a locking fault, the boiler will try to clear itself.

Common Causes

  • Circulation pump issue
  • Air in the system
  • Blocked heat exchanger
  • Faulty flow temperature sensor

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    Check for any air locks in the system, potentially by bleeding radiators if applicable.

  2. 2

    Allow the boiler to attempt an automatic reset.

  3. 3

    If the fault persists, contact a qualified service technician to check the pump and sensors.

Browse all codes in this manual (43)
Verified technical data. Last updated: April 2026

Related Faults

--/Flashing --/ - Communication fault between UBA 3 and BC10 controller0/y/Locking fault 0/y/ (2/8/5) - Return temperature sensor detected over 203°F (95°C)1/a/Blocking fault 1/a/ (3/1/6) - Flue gas sensor temperature too high
Source: Buderus Logamax plus Boilers
Open Manual (Page 47)Search more codes in this manual