Functional Scheme - Bosch 520PN Applications Manual

50 | Functional scheme

12 Functional scheme
Water flow
> 0.5 gpm
(> 1.9 l/min)
(see WF calc.)
Fan speed = correct
Ionization = off
Temp. limiter = closed
Temp. sensors = ok
Over heat protection = ok
INPUTS:
- FANSPEED
- WATER TEMP.
- WATERFLOW
OUTPUTS:
- FANSPEED
- WATERFLOW
close one gas
valve
flame off?
NO
YES
Fig. 75 Functional scheme
6 720 644 887 (2013/02)
IDLE
water tap
NO
open?
YES
Appliance
NO
ready to start?
YES
NO
waiting
Fan speed
time of 10s
NO
OK?
passed?
YES
Start sparking
Open the gas
NO
valve
1st
Safety time
Ionization
NO
of 5s passed?
detected?
YES
Hot water
delivered at
selected temp.
YES
safety
NO
devices
OK?
YES
water tap
closed
NO
<0.5 gpm?
YES
NO
waiting
time of
YES
close second
1s passed?
gas valve
Post purge of
fan for 7 sec.
YES
NO NO
2nd
Safety time
Safety time of
YES YES
of 5s passed?
5s passed?
Water flow
Calculus
Minimum Power
WF =
(Set point - Inlet)
6720608158-65.2V
0.5 GPM < WF < 1.6 GPM
(2 l/min < WF <6 l/min)
YES
Burner ON
Burner shutdown at:
Set point +9°F (5°C)
WF < 0.45 gpm ± 0.05 gpm
(WF < 1.7 l/min ± 0.2 l/min)
Water flow procedure
See error code table
3rd
YES
See error
code table
Post purge of
fan for 7 sec.
Stay blocked
till RESET
NO
WF > 1.6 GPM
NO
(WF > 6 l/min)
YES
Burner ON
Burner shutdown at:
Set point +14°F (8°C)
WF < 0.45 gpm ± 0.05 gpm
(WF < 1.7 l/min ± 0.2 l/min)
C 1210 ES/ESC