Operational Flow Diagram - Worcester 25Si Installation And Servicing Instructions

17. Operational Flow Diagrams
CENTRAL HEATING FUNCTION
MAIN SWITCH
CH light On.
Pump On.
CENTRAL Fan ON/
HEATING ignition
DEMAND Sequence.
Burner Light
Three minute
wait
DOMESTIC HOT WATER FUNCTION
MAIN SWITCH
DOMESTIC
HOT WATER
Is CH
DEMAND
interrupted?
(Priority over
CH demand)
DHW temp
drops to user
set point
Primary
75°
Green Light
ON
Two minute
minimum
burner
pressure then
ramp up
pressure over
next one
On.
minute
Gas valve Off.
(CH light still
on. Pump still
On)
Green Light
ON On
Pump continue
4 seconds if
primary temp
YES
above DHW
setting. Burner
to MAX for 4
seconds
NO
Ignition
sequence and
burner to MAX
for 4 seconds
Gas valve off.
Fan on 35
seconds.
Pump on until
temp drops to
60°C
Gas valve off.
Fan on.
Pump on
Room
thermostat
and/or mains
programmer
(or link) On
AND
AND
Electronic
facia
On
programmer
(if fitted) On
AND
AND
ST13 link in
AND
AND
CH control
knob On
Modulate gas
to maintain
flow
temperature
set by control
knob
Over tempera-
ture shut-
down if flow
temperature
5°C above set
value
Flow switch
On
(Tap open)
Modulate gas
to maintain
delivered
water
temperature
set by control
knob
Over
temperature
shut-down if
water
temperature
above 85°C
Primary
temperature
115°C
30
DEMAND Overrun
END function
(see overleaf)
Overrun
DEMAND
function
END
(see overleaf)