Worcester 24CDi BF, Installation And Servicing Instructions

13.1 SUMMARY

The appliance is dispatched with the controls set to provide a
maximum output for domestic hot water and central heating of
24 kW (81,900 Btu/h).
The appliance automatically modulates to satisfy lower heat loads.

Domestic Hot Water Circuit

Confirm that the mains water supply has been flushed out at
installation. If not it will be necessary to disconnect the cold
water inlet pipe from the appliance and thoroughly flush.

Central Heating System

Confirm that the system has been fully flushed out at installation
using a flushing agent. Flush the system before starting to
commission the appliance and, at the end of the commissioning
procedure, add a suitable flushing agent and drain whilst hot.
Immediately refill and re-pressurise.

Gas Service. The complete system, including the meter, must be
inspected and tested for soundness and purged as indicated in
BS 6891. In the event of a leak, or suspected leak, at the ‘O’ ring
joint on the main appliance manifold, connect a manometer to
the test point on the inlet of the multifunctional gas valve. A
soundness test carried out after turning off the appliance gas
cock will test the section between the gas cock and the gas
valve, thus enabling the leak to be traced to either a visible joint
or to the ‘O’ ring.
13.2 APPLIANCE AND CENTRAL HEATING

SYSTEM – PREPARATION

Remove the cabinet front panel.
Check that the electrical supply and the gas service to the
appliance are off.
Check that all the water connections throughout the system are tight.
Open the system valves at the appliance. Open all the radiator
valves, fill the system and vent each radiator in turn.
Remove the bottom panel to gain access to the filling loop
assembly. (The grey knob for the filling loop is packed in the
hardware pack and should be fitted as shown in Fig. 6,6a.
Insert the bayonet end of the filling key into the corresponding
cutouts in the filling loop housing and twist to lock the key in place.
Turn the grey knob anti-clockwise to allow water ingress and fill
until the pressure gauge reads 2.5 bar.
Turn the grey knob clockwise to stop filling and remove the filling
key by lining up the bayonet end of the key with the cutouts in
the filling loop housing and withdrawing the key.

N.B. The key must always be removed from the filling loop
housing after the system has been filled to prevent accidental
filling and to comply with Byelaw 14 of the Water Byelaws
Scheme.

Store the key in a safe place for future use and refit the bottom
panel.   
The automatic air vent will vent the appliance. Check that the air
vent cap has been loosened. Refer to Fig. 28.
Check that the pressure relief valve operates by turning the knob
anti-clockwise until it releases. Water should be expelled from
the discharge pipe. Refer to Fig. 22. 
Lower the facia panel to gain access. Refer to Section 15.3, c.

Set the Expansion Vessel Pressure

The charge pressure of the expansion vessel as dispatched is 0.5
bar, which is equivalent to a static head of 5 metres (17 ft). The
charge pressure must not be less than the static head at the
point of connection. Refer to Fig.18.  A Schraeder type tyre valve
is fitted to the expansion vessel to allow the charge pressure to
be increased if necessary.

Set the System Pressure

Release water from the system using the relief valve test knob
see Fig. 22, until the system design pressure is obtained, up to a
maximum of 1.5 bar.
Initial system design pressure (bar) = Expansion vessel charge
pr 0.3 bar.

NOTE:

1 bar is equivalent to 10.2 metres (33.5ft) of water.

Set the movable pointer on the pressure gauge to coincide with

the indicating pointer giving a permanent record of the set system
pressure.
If the pressure indicated on the pressure gauge is greater than 2.6
bar when operating at the maximum central heating temperature,
an extra expansion vessel must be fitted to the system as close as
possible to the appliance central heating return connection.
The appliance (as dispatched) can accommodate a system volume
of about 83 litres. Refer to BS 7074 Part 1. If the system volume is in
excess of that accommodated by the expansion vessel fitted to the
appliance then an extra vessel must be fitted as close as possible to
the central heating return connection of the appliance.
Any extra vessel fitted must be pressurised to the same figure as
the integral vessel. If the expansion vessel fails then the specified
replacement must be fitted. 

13.3 PROGRAMMER

Any programmer fitted on the appliance should be set up at this
stage following the instructions sent with the programmer.
The programmer will retain the setting for up to three weeks
following an interruption in the electricity supply.

13.4 APPLIANCE OPERATION

Turn off the gas and electricity supplies to the appliance.
Loosen the burner pressure test point screw on the gas valve and
connect a pressure gauge. See Fig. 23.
Undo the two screws and hinge down the facia to gain access to
the mode switch. 

Domestic Hot Water

Set the gas valve mode switch, at the rear of the facia, to the
maximum position. 
Turn on the gas and electricity supplies.
Set the CH temperature control knob fully anti-clockwise to               
and the DHW temperature to MAX.
Open a hot water tap.
A continuous ignition spark will occur until the burner is alight and
sensed by the control circuit. The burner pressure should be
13.2mbar for natural gas. If the burner pressure cannot be
achieved then check that the inlet pressure at the appliance is
20mbar for natural gas. This is equivalent to a 18.5-19.0 mbar
(G20) at the gas valve.  

13. Commissioning

15

Auto air
vent

(Remove cap)

Fig. 20. Appliance casing and control

equipment fixings.

Inner casing cover
fixing screws (4)

Side casing
fixing
screws (4)

Facia panel
fixing
screws (2)

Bottom
facia panel
fixing
screws (3)