Viessmann Vitotwin 300-W Installation And Service Instructions For Contractors page 136

Troubleshooting
Fault messages
Fault mes- Cause
sage
"396: Eng Deviation in actual thermo-
head t'c' couple values.
cont integ"
"397: Eng
head t'c'
cont rise"
"398: Eng
head t'c' lim
integ"
"399: Eng
head t'c' lim
rise"
"400: Flow Captured return temperature
dir heat (code 8314) higher than flow
gen" temperature (code 8310).
"421: Temp Captured return temperature
diff h'ex eng (code 8314) higher than flow
bu" temperature (code 8310).
136
(cont.)
Remedy
Check spring length; adjust if
necessary (see page 77).
Check plug-in connection
X205 and thermocouple con-
necting cables.
Check the temperature dif-
ferential at the Stirling head
thermocouples in steady-
state condition (code 7764
and 7764 in input/output
test). If the differential
> ± 50 K, reposition the ther-
mocouples (remove yellow
connection plug and plug in C
to L or L to C). Then check
electrical output (code 8200
in diagnostics engine). If the
electrical output is too low,
replace the thermocouples.
Check sensor leads.
Check control unit PCB and
replace if necessary (see
page 138).
Check whether there is a
min. flow rate of 240 l/h (code
8366 in diagnostics heat gen-
eration).
Check plug-in connection
X205 and thermocouple con-
necting cables. Check ther-
mocouples, replace if neces-
sary (see page 149).
Check cable harness.
Check function of the circula-
tion pump.
If the fault has not been rec-
tified, replace the PCB (see
page 138).
Re-
set-
ting
AR (5
s)
AR
(
20 min
)
AR (5
s)
AR
(
20 min
)
AR