Sime Format B, Installation And Servicing Instructions

– Turn the main selector switch on and off a few times (with

the hot tap still open) and check that the pressure returns
to the correct (set) maximum value (as in 

Table 3).

– Set the minimum burner pressure by first isolating the

electricity supply and disconnecting one of the modulating
solenoid leads, then restore the electricity supply and fully
open a DHW tap to light the appliance at minimum gas
rate.

– Set the minimum pressure with reference to 

Tables 3 by

holding nut (B) in position with a 10 mm spanner  and
rotating the plastic screw (A) with a screwdriver until the
correct pressure is obtained. Turn the screw clockwise to
increase the pressure or anti-clockwise to decrease it. It is
essential that the max pressure has been set prior to
adjusting the minimum pressure. Check that the minimum
pressure is correctly set by turning on and off the D.H.W.
inlet valve several times and ensuring that the pressure
returns to that previously adjusted;

– Isolate the power supply, re-connect the modulation lead,

restore the power and re-check the maximum pressure,
then re-fit the plastic cover (1).

– Reduce the D.H.W. draw off rate to the minimum nec-

essary to maintain the burner alight by carefully adjusting
the D.H.W. Inlet valve and check that the burner pressure
decreases in response to D.H.W. temperature rise. Fully
open the inlet valve;

– Close the D.H.W. tap and ensure that the burner is

extinguished and the pump stops.

– Adjust the Central Heating maximum pressure as

described in section 4.3, then complete the re-
commissioning as described in 4.4 and 4.5.

8.7

AIR PRESSURE SWITCH

– Remove the casing front panel and sealed chamber front

panel as described in section 5.1.

– Disconnect the pressure sensing pipe from the switch.
– Remove the switch (two screws) and fit the new one.
– Transfer the electrical connections one at a time (to

ensure that they are not incorrectly re-fitted) to the new
switch.

– Re-assemble in reverse order referring to the wiring

diagrams (section 7) if necessary. Ensure that the
pressure sensing lead is correctly connected to the low
pressure connection on the pressure switch (marked P2).

8.8

SAFETY THERMOSTAT

The safety thermostat is situated on the flow pipe (3 fig. 3).
– Remove the casing front panel as described in section 5.1.
– Disconnect the two limit thermostat wires.
– Unscrew the two limit thermostat fixing screws and

remove the thermostat.

– Replace the thermostat and spread heat sink compound

(supplied) over the base of the new one.

– Re-assemble in reverse order (Polarity is immaterial).

8.9

THERMISTOR

The thermistor is placed over the main exchanger. 
– Remove the casing front panel as described in section 5.1.
– Isolate the C.H. flow and return valves (20 - 19 fig. 2), and

drain the appliance through the drain plug (16 fig. 2).

– Pull off the electric connection, and unscrew the

thermistor from the exchanger.

– Replace the thermistor and re-assemble in reverse order.

Table 8 shows the resistance values (

Ω

) that are obtained on

the sensor as the temperature varies.

8.10

DRIVER PCB

– Remove the casing front panel as described in section 5.1.
– Open the control panel protecting cover by removing the

four fixing screw.

– Pull off the potentiometer knobs.
– Release the PCB (6 screws), transfer all connections onto

the new PCB, and re-assemble in reverse order.

8.11

PUMP MOTOR

– Remove the casing front panel as described in section 5.1.
– Unplug the electrical connection plug.
– Isolate the C.H. flow and return valves (20 - 16 fig. 2), and

drain the appliance through the drain plug (16 fig 2).

– Unscrew the four fixing screws on the motor.
– Replace the pump motor and re-assemble in reverse

order. If the new pump is fitted with a speed adjuster,
ensure that the speed is set to maximum.

– Refill and commission the system as described in section 4.1.

8.15

C.H. EXPANSION VESSEL

Replacement is not recommended if a rear flue outlet is used
or if the clearance above the casing is less than 300 mm.
– Remove the casing front panel as described in section 5.1.

32

Temperature (°C)

Resistance (

Ω

)

20

12,090

30

8,313

40

5,828

50

4,161

60

3,021

70

2,229

80

1,669

TABLE 8

KEY
A

Plastic screw

B

Nut

C

Sealing cap

Fig. 29