Instructions To The User - Worcester 24CDi Installation And Servicing Instructions

sensed by the control circuit. The burner pressure should be 14.8mbar
(24CDi) or 15.5mbar (28CDi) or 13.5mbar (35CDi II ) for natural gas and
35.5mbar (24/28CDi) or 34.7mbar (35CDi II) for propane. If the burner
pressure cannot be achieved then check that the inlet pressure at the
appliance is 20mbar for natural gas and 37mbar for propane. This is
equivalent to a 18.5-19.0 mbar (G20) or 36 mbar (G31) at the gas valve.
Set the gas valve mode switch to the minimum position.
The burner pressure will drop to the minimum setting which should be
1.5mbar (24CDi) or 1.0mbar (28CDi) or 0.9mbar (35CDi II) for natural gas or
5.4mbar (24CDi) or 3.8mbar (28CDi) or 3.1mbar (35CDi II) for propane.
Test for gas soundness at the joint between the burner and the gas valve
with leak detection fluid.
NOTE: The burner pressure is factory set and if (after checking that the
supply pressure is sufficient) the correct pressure is not obtained then
Worcester Heat Systems Service Department should be contacted.
If the appliance does not light, check that it is not in the 'lockout' state by
pressing the lockout reset button. See Fig. 30.
Set the gas valve mode switch back to the normal position and refit the facia.
Turn off the electricity supply, and then back on again to reset the controls.
Gradually close the hot tap and check that the burner pressure drops. Fully
open the tap and check that the burner pressure rises. Fully close the tap
and check that the burner goes off. The fan may continue running until the
appliance has cooled to a preset temperature.
Set the Operating Switch to OFF.
Central Heating
Check that all the radiator valves are open. Set the room thermostat and
the Central Heating Temperature Control to maximum. Set the DHW
temperature control to MIN.
On sealed systems check that the system is pressurised and set to the
required pressure as indicated on the gauge.
Set the Programmer, if fitted, to HEATING & WATER.
Set the operating switch to ON.
The burner will light.
The appliance will modulate its output from 9.0 to 24.0 kW (24/28CDi) or
10.5 to 27.5 kW (35CDi II) over a period of about two minutes.
Check the system to ensure that all the radiators are heating up evenly. If
not then bleed each radiator through its vent screw.
Shut down all but one of the radiators and observe the burner pressure fall.
Open all of the radiator valves and check that the burner pressure rises.
Balance the system so that the required temperature difference across the
central heating flow and return pipes is obtained. See Table 3.
Adjust the central heating by-pass valve until the same temperature
difference is obtained. See Fig. 29. This should be carried out with only a
single radiator operating. If thermostatic radiator valves are fitted then one
radiator should be left uncontrolled. The bypass valve should never be fully
closed.
Set the room thermostat to minimum and check that the burner goes out.
Reset the room thermostat to maximum and the burner will re-light and
follow the normal operating procedure.
Check for proper ignition of the burner after a break in the gas supply. Turn
off the gas service cock and wait for 60 seconds. The burner will go out but
sparking from the electrode will continue for 10 seconds when the
appliance will enter a 'lockout' state. Carefully open the gas service cock,
press the lockout reset button and observe the burner re-light and follow
the normal sequence of operation. Refer to Fig.30.
Set the Operating Switch to OFF.
Turn off the gas service cock and the electrical supply to the appliance.
Drain the system while the appliance is still hot.
Refill, vent and, with a sealed system, re-pressurise as described in Section
13.2.
Domestic Hot Water and Central Heating
Turn on the electricity supply to the appliance and open the gas supply
cock at the appliance.
Set the Operating Switch to ON. If a programmer is fitted, set the domestic
hot water to Continuous or 24Hrs and the central heating to ON. The burner
will light and heat will pass into the system. Set the DHW temperature to
MAX and turn on a hot water tap and check that fully heated hot water is
discharged from the tap.
Close the tap and the burner will go off. The appliance will then return to
the central heating mode and automatically balance with the system
requirements.
Set the Operating Switch to OFF and the burner will go out.
12.5 COMPLETION OF COMMISSIONING
Disconnect the pressure gauge from the gas valve and tighten the test
point screw.
Restart the appliance and check for gas soundness around the test point
screw.
Refit the cabinet front panel.
If the appliance is being passed over to the user immediately, refer to
Section 14 - Instructions to the User.
If the appliance is to be left inoperative, check that the Operating Switch is
set to OFF. Turn off the gas service cock.
For short inoperative periods, leave the appliance under the control of the
built in frost thermostat or the remote frost thermostat (if fitted) or leave
operating continuously with the room thermostat set at 6°C
Do not switch off the electricity supply.
If there is any possibility of the appliance and the system being left totally
unused in freezing conditions then switch off the gas and electricity and
drain the appliance and the system.
Fig. 29. Central heating by-pass adjustment.

14. Instructions To The User

Fig. 30. User controls.
C.H. demand
indicator
Mains
indicator
Mains C.H. temp
switch control
knob
14.1 Tell the user how to operate the appliance and hand over
the Users Instructions leaflet and Benchmark log book.
14.2 Tell the user what to do if the heating system is not to be
used in frosty or freezing weather.
14.3 Tell the user the sealed system set pressure.
14.4 Tell the user of the importance of regular servicing.
Worcester Heat Systems Ltd. offer a comprehensive maintenance
contract.
14.5 Set the system controls to the user's requirements.
14.6 If an external programmer has been fitted which has a
programmable domestic hot water facility then it is suggested
that this be set to Continuous or the equivalent.
14.7 Tell the user about the safety devices and hazard notices.
19
D.H.W. demand
indicator
Reset Flame
button indicator
D.H.W.
temp control
knob
System
pressure
gauge