Worcester 24CDi Installation And Servicing Instructions Download Page 3

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The clearances specified for servicing must be maintained. Refer
to Fig. 2.

2.6 Flue

The appliance has a multi-directional horizontal fanned flue system.
The standard telescopic flue assembly accommodates flue
lengths from 297mm to 725mm.
Extension flue lengths available are from 726mm up to 4000mm
(24CDi) or up to 3000mm (28CDi and 35CDi

A vertical flue assembly kit is available.
Optional 45° and 90° flue bends are available.
A terminal guard, Type K2, GC 393 553, is available from Tower
Flue Components, Vale Rise, Tonbridge,TN9 1TB.
Do not allow the flue terminal fitted to the outside wall to
become obstructed or damaged.
A kit for the internal fixing of the flue is available separately.

2.7 Controls

The ON/OFF switch will turn the mains electricity on and off at
the appliance.

Note:

There is still a live connection to the appliance.

The  electronic  control  system  and  gas  valve  modulate  the  heat
input in response to the central heating and domestic hot water
temperature settings.
The  Central  Heating  Temperature  control  knob  provides  for  the
selection of domestic hot water only (turned fully anti-clockwise)
or central heating and domestic hot water (turned clockwise).
The position of the Domestic Hot Water control knob will determine
the temperature of the water delivered to the tap or shower or bath.
A  choice  of  facia  mounted  programmers  are  available  as  optional
extras.  A  remote  mounted  programmer  may  be  connected  to  the
appliance.
The integral facia displays indicate the status of the appliance.
There  is  provision  for  the  connection  of  a  mains  voltage  room
thermostat and/or a frost thermostat.
The electronic controls prevent rapid cycling of the appliance in
the central heating mode.

2.8 System Notes

IMPORTANT: Check that no dirt is left in the water pipework
as this could cause damage to the appliance. Thoroughly
flush the heating system and the cold water mains supply in
accordance with the recommendations of BS7593: 1992.

Remove all system cleanser before adding any inhibitor.
The water pipe connections throughout a sealed system must be
capable of sustaining a pressure of up to 3 bar.
Radiator valves must conform to the requirements of BS 2767:1991.
The relief valve discharge must be directed away from any electrical
components or where it would cause a hazard to the user.
A drain cock to BS 2879 must be fitted to the lowest point of the system.
For circuit design purposes it is important that due note is taken of
the information given in Table 3 relating to the available pump head.

2.9 Showers, Bidets, Taps and Mixing Valves

Hot and cold taps and mixing valves used in the system must be
suitable for operating at the mains pressure.
Thermostatically controlled or pressure equalising shower valves
will guard against the flow of water at too high a temperature.
If a pressure equalising valve is used, set the Domestic Hot Water
temperature control knob to the ‘MAX’ position.
Hot and cold mains fed water can be supplied direct to an over-
rim flushing bidet subject to local Water Company requirements.
With all mains fed systems the flow of water from the individual
taps  will  vary  with  the  number  of  outlets  operated
simultaneously and the cold water mains supply pressure to the
property.  Flow  balancing  using  ‘Ball-o-Fix’  type  valves  is
recommended  to  avoid  an  excessive  reduction  in  flow  to
individual  outlets.  For  further  information  contact  Worcester
Heat Systems Technical Helpline.

2.10 Safety Considerations

The appliance must not be operated in a waterless condition.

The appliance must not be operated with the boiler inner casing
cover removed.
Work must not be carried out on the appliance without the gas
and electricity supplies being switched off.
Checks must be made to ensure that, where applicable, the
ventilation openings made into walls and partitions are of the
correct size and are not obstructed.

IMPORTANT:  Where  back-flow  prevention  devices,  including
water meters, are fitted the expansion of hot water into cold
water  main  can  be  prevented.  This  can  result  in  a  pressure
build-up that may cause damage to the boiler and household
devices such as showers, washing machines etc.
In  these  cases  we  recommend  that  a  mini-expansion  vessel
be fitted adjacent to the boiler in the cold water pipe.
2.11 Operation
Domestic  Hot  Water:

With a demand for hot water the burner

will light at its maximum setting and then automatically adjust
its output to maintain the temperature of the delivered water.
When hot water is no longer required, the burner will extinguish.
The fan and pump may continue to run for a short period to
dissipate the residual heat from the appliance.

Central Heating:

With a demand for heating the burner will light

at  its  minimum  setting  and  gradually  increase  to  give  the
maximum  output.  The  output  of  the  appliance  is  then
automatically  adjusted  to  maintain  the  temperature  of  the
system. The output can reduce down to its minimum of setting.
If  the  system  no  longer  requires  even  the  minimum  output  to
maintain  the  desired  room  temperature  the  burner  will
extinguish. The fan and pump may continue to run to dissipate
the  residual  heat  from  the  appliance.  The  appliance  will  remain
off  for  a  fixed  period  of  three  minutes  before  re-lighting  to
automatically meet the system requirements.

Domestic Hot Water and Central Heating:

The appliance will

supply heat to the central heating system as required. A demand
for  domestic  hot  water  at  a  tap  or  shower  will  override  the
central  heating  requirement  for  the  period  of  the  domestic  hot
water  demand.  When  hot  water  is  no  longer  required  the
appliance will return to the central heating state and its normal
mode of operation. The fan may continue to run to dissipate the
residual heat from the appliance as necessary.

Fig. 1. Appliance water flow diagram.

Boiler

6 7 8 9 10

1. Automatic air

vent.

2. Gas to water

heat
exchanger.

3. Circulating

pump.

4. Water to water

heat

exchanger.