Room
thermostat
and/or mains
programmer
(or link) On
facia
programmer
(if fitted) On
CH control
knob On
33
18. Operational Flow Diagrams
MAIN SWITCH
ON
CENTRAL
HEATING
DEMAND
Pump on.
Fan ON/
ignition
sequence.
Burner Light
On.
Three minute
wait
Gas valve Off.
Burner light
off. (Pump still
On)
Over tempera-
ture shut-
down if flow
temperature
5°C above set
value
19 second
minimum
burner
pressure then
ramp up
pressure over
next one
minute
Modulate gas
to maintain
flow
temperature
set by control
knob
(50-82°C)
DEMAND
END
Overrun
function
(see overleaf)
CENTRAL HEATING FUNCTION
AND
AND
DOMESTIC HOT WATER FUNCTION
MAIN SWITCH
ON
Flow sensor
signal
(Tap open)
DOMESTIC
HOT WATER
DEMAND
(Priority over
CH demand)
Pump continue
4 seconds if
primary temp
above DHW
setting. Burner
to MAX.
Modulate gas
to maintain
delivered
water
temperature
(55°C)
Is CH
interrupted?
DHW temp
drops to
<55°C
Over
temperature
shut-down if
water
temperature
above 80°C
Primary
temperature
94°C
DEMAND
END
Overrun
function
(see overleaf)
YES
NO
Ignition
sequence and
burner to MAX
Gas valve off.
Primary
78°C
Gas valve off.
Pump on
