6 720 611 449 GB (03.11)
Appendix
47
10.5 Operational Flow diagrams
10.5.1 Central heating function
Fig. 61
6 7
20 6
10 5
76 - 26.TD
Ye
s
No
Ye
s
No
Mains
switc
h
ON.
Green
light
ON.
Room
thermost
at
and/or mains
programmer or
link O
N
AN
D
Electronic facia
programmer (
if
fitted
) O
N
AN
D
C
H
control
knob ON.
CH
demand
.
Burner remains O
FF
until flow temperature
is below set value
.
Gas valve shuts
.
Pump remains O
N
.
Over temperature
shut down if water
temperature is 5°C
above set value
.
Pump O
N
Fan to
st
art speed
. Gas
valve opens
.
Burner
st
abilises at
st
art speed for
5-1
0 secs
Fan speed
reduces
over 1
5
secs
.
Fan min
.
speed for
9
0 secs
.
B
oiler
unused
for long
period
.*
*Minimum
heat
input f
or
15
m
in
.
B
oiler
operates to
matc
h
system load
and C
H
control
setting
.
Ignition sequence
Ignition spark for
5 seconds
.
Burner lights
. Red
light O
N
.
Repeats 5 times
(N
.G
.) or 3 times
(L.P
.G
.) before
loc
k-out
.
Fan runs to
purge gas from
burner
.
C
H
demand
satisfied
.
Gas valve closes
.
Red light O
FF
.
Pump and Fan
run for up to 3
mins
.
* N
O
TE
: T
he sequence ensures that the condens
ate siphon is not empty
after long
OFF
periods
. (
More than 24 hours without a demand
).
