Worcester 25Si Installation And Servicing Instructions page 23

Fig.45 . Lower casing - gas and water
controls.
Air flow switch
Water flow
switch
Red tube
(+ve)
Clear tube
(-ve)
Earth
connection
Transformer
Switch on the gas and electricity supplies. Check for gas
tightness at the gas valve inlet.
Refer to Section12-Commissioning for the method of checking
the pressures.
Check for gas soundness at the gas valve outlet.
Adjust the maximum and start pressure [minimum], as
necessary, to obtain the required pressures.
Switch off the appliance and disconnect the pressure gauge.
15.4.2 Spark Electrode
Remove the inner casing and the combustion chamber.
Carefully pull off the leads from the electrodes. Loosen the screw
and remove the spark electrode assembly. Refer to Fig 46.
Fig.46. Spark electrode assembly
Notched to aid
location in the fixing bracket
Burner blade
assembly
Fixing bracket
Fixing screw
15.4.3 Flame Sense Electrode
Remove the inner casing and the combustion chamber.
Carefully pull off the lead from the electrode. Loosen the screw
Spark electrode lead
Spark
electrode
NOTE: Cross- lighting
strips are not
shown
Spark electrode
assembly
Gas Valve
1
Fig.47. Flame sense electrode
Notched to aid
location in the fixing bracket
Burner blade
assembly
Fixing bracket
Fixing screw
and remove the flame sensing electrode assembly. Refer to Fig
47. Ensure that the electrode is at the correct height above the
burner blade.
15.4.4 Burner
Remove the inner casing and the combustion chamber.
Remove the electrode connections.
Release the union connection beneath the burner and remove
the burner from the appliance. Refer to Fig 44.
Do not omit the gasket when fitting the new burner.
15.4.5 Combustion Chamber Insulation
Remove the burner as described in 15.3.4 preceding.
Remove the primary heat exchanger as described in 15.4.21
following.
Replace the side and front pads in the combustion chamber
assembly. Refer to Fig 48.
Replace the rear insulation pad.
23
Pump connection
Expansion vessel con-
nection
Pump
Pump connection
Pressure gauge
Relief valve
Boiler drain
connection
Facia assembly
Flame sense
electrode
NOTE: Cross- lighting
strips are not
shown
Flame sense
electrode assembly