Vaillant ecoTEC sustain 24 Installation And Maintenance Instructions Manual page 51

Fault code Meaning
F.72 Fault: Deviation in the water pressure
sensor/return temperature sensor
F.73 Fault: Water pressure sensor not con-
nected or has short-circuited
F.74 Fault: Electrical problem in the water
pressure sensor
F.77 Fault: Condensate or smoke
F.83 Fault: Dry fire
F.84 Fault: Flow/return temperature sensor
F.85 Fault: Temperature sensor
F.87 Fault: Ignition transformer cable
F.88 Fault: Gas valve assembly
F.89 Fault: Pump
F.97 Fault: Main PCB self-test failed
Err Fault: Interface communication
0020253094_05 ecoTEC sustain Installation and maintenance instructions
Possible cause
Flow/return NTC temperature difference too great → flow and/or return tem-
perature sensor defective
Interruption/short circuit of water pressure sensor, interruption/short to earth
in supply pipe to water pressure sensor or water pressure sensor defective
Line to water pressure sensor has a short circuit to 5 V/24 V or internal fault
in the water pressure sensor
Applies to: Installed condensate pump or flue non-return flap (optional)
Check the defective condensate pump or flue non-return flap
When the burner starts, the temperature change recorded by the flow or
return temperature sensor is non-existent or too small: Insufficient water in
the product, flow or return temperature sensor incorrectly attached to the
pipe
Values not consistent, difference between flow and return < -6 K
Flow and return temperature sensors signalling implausible values: Flow and
return temperature sensors have been inverted, flow and return temperature
sensors have not been correctly installed
The flow and/or return temperature sensors have been installed on the same
pipe/incorrect pipe
Temperature sensor not connected or is connected incorrectly
Ignition transformer cable harness not connected to the main PCB or it is
connected incorrectly, short circuit in the cable harness or damaged ignition
transformer
Gas valve assembly not connected or it is connected incorrectly, short circuit
in the cable harness
Pump not connected or it is connected incorrectly, incorrect pump connec-
ted, short circuit in the cable harness
Main PCB defective
Interface PCB not connected or connected incorrectly, short circuit in the
cable harness
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