Operational Flow Diagrams - Worcester 24CDi Installation And Servicing Instructions

18. Operational Flow Diagrams

CENTRAL HEATING FUNCTION
MAIN SWITCH
CH light On.
Pump On.
Fan ON High for 2
sec then Low speed -
CENTRAL
28CDi.
HEATING
Fan ON High for 2
DEMAND
sec then Low speed -
35CDi II.
Ignition Sequence.
Burner Light On.
Three minute
wait
DOMESTIC HOT WATER FUNCTION
MAIN SWITCH
ON
HW light On.
Pump On.
DOMESTIC Fan ON High speed -
HOT WATER 28CDi.
DEMAND Fan ON High for 2
(Priority over sec then Low speed
- 35CDi II.
CH demand)
Ignition Sequence.
Burner on
Ten second
wait
Green Light
ON On
Two minute mini-
mum burner
(30 seconds -
35CDi II
)
pressure then
ramp up
pressure over
next one minute
Gas valve Off.
(CH light still
on. Pump still
On)
Green Light
On
Four second
ramp to max.
gas pressure.
Fan speed
changes at mid
pressure
35CDi II
.
Gas valve Off.
(HW light still
on. Pump still
On)
Room
thermostat
and/or mains
programmer
(or link) On
AND
AND
Electronic
facia
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
at value set by
control knob
Over
temperature
shut-down if
water
temperature
8°C above set
value
Burner shut-
down if
primary
temperature
94°C
(until 84°C)
29
Pump
continue four
DEMAND minutes.
END Fan continue
fifteen
seconds
Fan continue
fifteen
seconds
DEMAND
END
Possible
overrun
condition
within next
four minutes
(See next
section)