Error 26.26: Outside sensor
LambdaControl 1
Error 26.26
Outside sensor
Cause: Wrong indicated values
Display 4 amber: illuminates
Information text: Limited operation
Emergency program: YES
Reset: Automatically after error correction
Error detection: Controller measures a temperature of >60°C (interruption) or < -50°C (short circuit) at sensor input ST4 (KL4 – 5).
Check setting 10.06 Outside sensor “YES” / “NO”.
Rectification: Call service technician – possible causes:
1. Test – are plug ST4 and the 16-pin plug properly connected with the controller and is the sensor connected correctly? Is
that the case, continue with test 2.
2. Test – outside sensor: Remove plug ST4. Check for a resistance of 2155.9Ω at plug ST4 (KL4 – 5) at 20°C and a resistance
of 2770.1Ω at 100°C. Is that the case, continue with test 3.
3. Test – Connecting lead from plug ST4 to outside sensor: Check wires individually for continuity and short circuits against
each other. If the cable is OK, replace the outside sensor for testing purposes. If the error is not rectified, continue with
test 4.
4. Test – wiring harness: Remove the 16-pin plug from the controller. Check for a resistance of <1Ω between the 16-pin plug
(KL4) and plug ST4 (KL5); check for a resistance of <1Ω between the 15-pin plug (KL15) and plug ST4 (KL4). Is that not the
case, the system has a wiring error or the controller is defective.
Experience shows that the controller is usually only defective, if faulty wiring or spurious actions damaged the applicable
input/output.
Controller function: Heating circuits work with the outside temperature measured on the last failure-free day. Fuel calculation is
carried out without heating demand based on the available loading capacity.
Note 26.27: Flow rate too low
LambdaControl 1
Note 26.27:
Flow rate too low
Difference > 20K
Cause: Difference too large
Display 4 amber: illuminates
Information text: Increase load pump M1 speed
Emergency program: YES
Reset: Press button ► (refuel)
Error detection: The difference between the boiler flow and return is >20K for 60 minutes. This is the limit for a correct
accumulator charging – return and boiler temperature control.
User intervention: Increase the speed of the load pump M1 and check if all stopcocks are opened, or call a service technician.
Technician intervention: If no hydraulic errors can be detected, i.e. air in system or stopcocks not opened, the load pump M1
may be defective (electrical output too small, mechanical damage of wheel, etc.).
Controller function: The boiler output and the required boiler temperature value are reduced once 89°C is exceeded.
Error 26.28: Return temperature too low
LambdaControl 1
Error 26.28
Return temperature
too low
Cause: Return temperature too low
Display 4 amber: illuminates
Information text: Is return valve Y1 not closing?
Emergency program: NO
Reset: Press button ► (refuel)
Error detection: If the return temperature is lower than the required value after AFO ― with closed Y1― (for a period of 30
minutes) the error message is displayed.
Rectification: Call service technician – possible causes:
1. Test – Return control: Check proper function of Y1 with an aggregate test (see chapter 4.5). Be mindful of the fact that
foreign material, which is not visible from the outside, may interrupt the closing of the control valve. Also, remember that
heat extraction should only be done through the return system.
Controller function: Firing is possible.
Note: Rectify error immediately: Boiler perforation from corrosion possible.
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