Fault Codes - Viessmann FB2A Installation And Service Instructions For Contractors

Troubleshooting

Fault codes

Fault code System characteris-
on the dis- tics
play
10 Controls as if the out-
side temperature
were 0 °C
18 Controls as if the out-
side temperature
were 0 °C
20 Regulates without
flow temperature
sensor (low loss
header)
28 Regulates without
flow temperature
sensor (low loss
header)
30 Burner blocked
38 Burner blocked
40 Mixer closes
48 Mixer closes
50 No DHW heating
51 No DHW heating
58 No DHW heating
86
Cause
Short circuit, out-
side temperature
sensor
Lead break, out-
side temperature
sensor
Short circuit, sys-
tem flow tempera-
ture sensor
Lead break, sys-
tem flow tempera-
ture sensor
Short circuit, boiler
water temperature
sensor
Lead break, boiler
water temperature
sensor
Short circuit, flow
temperature sen-
sor, heating circuit
2 (with mixer)
Lead break, flow
temperature sen-
sor, heating circuit
2 (with mixer)
Short circuit, cylin-
der temperature
sensor
Short circuit, outlet
temperature sen-
sor
Lead break, cylin-
der temperature
sensor
Measures
Check the outside tem-
perature sensor (see
page 95)
Check the outside tem-
perature sensor (see
page 95)
Check the low loss header
sensor (see page 96)
Check the low loss header
sensor (see page 96)
Check the boiler water
temperature sensor (see
page 96)
Check the boiler water
temperature sensor (see
page 96)
Check flow temperature
sensor
Check flow temperature
sensor
Check sensors (see
page 96)
Check sensors (see
page 96)
Check sensors (see
page 96)