Worcester benchmark ZWB 7-25 R 25 HE Design, Installation And Servicing Instructions page 37

Diaphragm in mixer unit
B Take care not to damage diaphragm
(443) when removing and refitting it.
B Open mixer unit (29).
B Carefully withdraw diaphragm (443) from fan intake
tube and check for soiling and splits.
3.
1.
2.
6 720 610 790-07.2R
Fig. 57
B Carefully refit diaphragm (443) the correct way round
into the fan intake tube.
The flaps of the diaphragm (443) must
i
open upwards.
B Seal the mixer unit (29).
Condensation trap
In order to prevent spillage of condensate, the conden-
sation trap should be completely removed, (see
page 35, fig. 51).
B Unscrew condensation trap and check connection to
heat exchanger is clear.
B Remove condensation trap cover and clean.
B Fill condensation trap with approx. 1/4 l of water and
refit.
Electrode assembly
B Switch off the master switch.
B Pull off the leads from the electrodes. Refer to fig. 2.
B Unscrew the two fixing screws and carefully remove
the electrode assembly . Refer to fig. 50.
6 720 611 441 GB (03.11)
443
29
B Clean the electrodes with a non-metallic brush. (The
spark gap should be 4,5 mm ± 0,5 mm.)
B Replace and re-connect the assembly taking care not
to mislay the inspection window.
Siphon
B Unscrew the clip and disconnect the pipe to the
siphon.
B Remove the drain plug to drain the siphon.
B Unscrew the securing nut from beneath the side
facia and remove the siphon. Refer to figure below.
B Refit and prime the siphon.
Condensate
Drain
Siphon
Drain Plug
Fig. 58
Expansion vessel
The expansion vessel should be checked once a year.
B Depressurise appliance.
B If necessary, adjust expansion vessel charge pres-
sure to static head of the heating system.
Heating system pressure
Fill the system using the WRAS approved
i
filling loop.
B The pointer on the pressure gauge should be 1 bar.
B If the pointer is below 1 bar (when the system is
cold), water should be added until the pointer is
1 bar again.
B Max. pressure of 2.5 bar when the heating system
water is at maximum temperature must not be
exceeded. If this pressure is exceeded then an extra
expansion vessel must be fitted in the system return
as close to the appliance as possible.
B If the system does not retain the pressure, the expan-
sion vessel and the heating system should be
checked for leaks.
Maintenance
37