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2/u/

Locking fault 2/u/ (2/1/3) - Flow/return temperature difference too high (over 122°F / 50°C)

Buderus · Logamax plus Boilers

What does 2/u/ mean?

The temperature difference measured between the flow temperature sensor and the return temperature sensor is more than 122°F (50°C). This indicates a problem with heat distribution or water circulation. This is a locking fault.

Common Causes

  • Poor water circulation
  • Blocked pipes
  • Circulation pump issue
  • Air in the system

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    Check the system pressure and ensure it is adequate.

  2. 2

    Allow the boiler to attempt an automatic reset.

  3. 3

    If the problem continues, contact a qualified service technician to inspect the pump and system circulation.

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