Worcester Highflow 3.5 OF Installation And Servicing Instructions page 19

Fig. 22. Domestic hot water Domestic hot water
high limit thermostat
overheat thermostat
Safety valve
(g) Remove the complete union fittings from the heat bank.
Withdraw the expansion vessel. It will be necessary to
slightly displace the gas line. Protect the threads of the
gas line union.
(h) Refit the new expansion vessel after transferring the short
connector pipe assembly. Re-assemble the appliance in
the reverse order.
(j)
Refill the system and check for the correct operation of
the controls and for the gas soundness of all relevant
joints.
The following components can be replaced if the cabinet
top panel, front panel and inner casing are removed. See
17(a), (b) and (e) preceding.
12.
THE BOILER LIMIT THERMOSTAT
(SeeFig.15.)
(a) Remove the two M 5 taptite screws holding the limit
thermostat to the flow pipe.
(b) Unscrew the limit thermostat leads form the gas valve.
One is located at the rear of the gas valve. It will be
necessary to remove the pilot pipe to gain access to the
rear connection. The connecton is a hexagon nut and an
M 10 open ended spanner will be required to release the
nut to allow it to be unscrewed.
(c) Push the grommet situated in the side ofthe inner casing
inwards into the casing.
(d) Thread the limit thermostat leads through into the inner
casing and remove the thermostat.
(e) Fit the new limit thermostat connecting the lead and
grommet assembly in the reverse order. Take care not to
overtighten the rear connection. Finger tight plus a quarter
of a turn is sufficient.
NOTE: When fitting replacement thermostat it is important to
ensure that no foreign matter is present on the contact surfaces
of both the thermostat and the mounting bracket. During
manufacture thermal grease is smeared on the surfaces and
may be left.
The following components can be replaced if the cabinet
top panel, cabinet front panel, facia and the control box
cover are removed. See 17(a), (b),
(c)
and (h) preceding.
Check that the electrical supply has been disconnected.
13.
THE DWH TANK OVERHEAT THERMOSTAT
(See Fig. 22.)
(a) Disconnect the thermostat leads at the terminal strip. Refer
to the wiring diagram (Fig. 11) to ensure that the correct
leads are disconnected. Do not leave any leads loose in the
control box.
Fig. 23.
(b) Release the strain relief bush by compressing the loose
section of the bush and carefully withdraw the leads from
the control box.
(e) Remove the two M3 taptite screws holding the overheat
thermostat to the flow pipe.
(f) Fit a new thermostat and reconnect ensuring that the strain
relief bush has been replaced. Refer to the electrical wiring
diagram (Fig 11) to ensure the correct connections are
made.
NOTE: When fitting a replacement thermostat it is important
to ensure that no foreign matter is present on the contact
surfaces of both the thermostat and the mounting bracket.
During manufacture thermal grease is smeared on the surfaces
and may be left.
(g) Re-assemble the appliance in the reverse order.
14.
THE CENTRAL HEATING CONTROl
THERMOSTAT
(See Figs. 22 and 24.)
19
(a) Unscrew the two slotted M 5 screws located beneath the
control box and ease away the thermostat and pump delay
timer mounting bracket.
(b) Using a pair of long nose pliers pull the retaining clip from
the thermostat pocket situated in the flow pipe and remove
the thermostat phial.
(c) Remove the thermostat central clamping nut and washer.
(d) Pull off the two electrical connections from the rear of the
thermostat.
(e) Push the thermostat body back to disenqage the spindle
from the mounting bracket.
(f) Withdraw the thermostat threading the capillary through
the slot in the rear of the electrical control box.
(g) Fit the new thermostat and re-assemble in the reverse
order. The capillary of the replacement thermostat must
be uncoiled to assist its passage through the control box
opening. With the thermostat in position the excess
capillary must be recoiled, without tight bends, and
positioned so that it is beneath the combined
1
eed and vent
pipe but not in contact with any hot surface. Ensure that
the retaining clip is replaced into the thermostat pocket.