Buderus 800-24 Installation And Servicing Instructions page 39

Code Meaning
2P
Safety sensor rises faster than 5 °C/sec., blocked for 30 sec.
Possible
cause
1 Resistance in the installation is too high
2 Safety sensor is dirty or faulty
3 External domestic hot water tank is too small for the
boiler's capacity
Code Meaning
2U
Temperature difference between the flow and return sensors is too high, blocked for 30 sec.
Possible
cause
1 Resistance in the installation is too high
2 Problem with the pump or pump cabling
(no circulation)
3 Water pressure is too low in the system
4 Return sensor is defective or the cabling is faulty
Code Meaning
4A
Flow sensor exceeds 100 °C
Possible
cause
1 Flow sensor is dirty or faulty
2 There is a problem with the pump or pump cabling
(no circulation)
3 Water pressure is too low in the installation
Code Meaning
4C
F2 fuse malfunction, or flue gas thermostat active
Possible
cause
1 Water pressure is too low in the installation
2 Heat exchanger is dirty
3 Flue gas retarder faulty or missing
Subject to modifications resulting from technical improvements !
Installation and servicing instructions condensing gas boiler 800 - 24/29/43/60 and 800 - 24T25/29T25 H/V • edition 02/2006
Action
Check if not all (thermostatic) radiator valves are closed or
clogged with dirt
Check the safety sensor for dirt. Measure if resistance over
the sensor is correct. If not replace safety sensor by
temporarily with another one (see subsection 5.3.9 and
subsection 5.3.10)
Top up the system (see subsection 2.1.1)
Action
Check if not all (thermostatic) radiator valves are closed or
clogged with dirt
Check if the pump cabling is faulty or if the pump is stuck
(see subsection 5.3.7)
Top up the system (see subsection 2.1.1)
Measure the resistance of the sensor
(see subsection 5.3.12)
Action
Check the sensor, replace if necessary
(see subsection 5.3.9 and subsection 5.3.10)
Check if the pump cabling is faulty or if the pump is stuck.
Replace pump if necessary (see subsection 5.3.7 and
subsection 5.3.8)
Top up the system (see subsection 2.1.1)
Action
Top up the system (see subsection 2.1.1)
Check for a dirty heat exchanger and clean if necessary
(see subsection 4.1)
Check if the flue gas retarder is installed in the heat
exchanger
Servicing 5
Buderus • http://buderus-domestic.co.uk
39