30
17. Operational Flow Diagram
Facia
light
ON
BOILER
HEA
T
DEMAND
If HL st
at
has tripped,
4 second
dela
y
CH
only
demand
CH selected
on timer &
room calling.
In addition f
o
r
Y plan:
DHW
selected
on timer &
tank satisfied
or
DHW off
signal fr
om
timer
.
Pump
continues
fo
r
3
minutes
DEMAND
END
DHW
only
demand
DHW
selected
on timer
, t
ank
st
at calling
DHW &
C
H
demand
DHW & CH
selected on
timer
, t
ank
st
at calling,
ro
om st
at
calling.
Facia contr
ol
knob abo
ve
position 'I'
Fan
ON
Pump
ON
20
second
dela
y
R
eset
on
fa
ci
a
APS
ON
LOCK
OUT
(all outputs OFF
EXCEPT pump)
Gas v
alv
e
and
sparking
ON
Flame
sense
No flame
sense f
or
8
seconds
Burner ON.
This sequence
is cy
cled t
o
satisfy
temper
atur
e
set b
y
f
acia
contr
ol knob.
Temper
atur
e
Sensor disconnected.
Fan and burner OFF
.
Pump running.
Failed ignition
Ov
erheat of
gas t
o
w
ater
heat ex
changer
Ov
erheat
thermost
at
trip.
Gas v
alv
e not
ener
gised during
ignition r
ecy
cle.
Burner
LOCK
OUT
R
eset
using f
a
cia
red butt
on
CH
= Central Heating
DHW = Domestic Hot W
ater
Pr
otection Sy
stems