Technical data

14.0 Changing Components

14.20 Central Heating Differential Valve

(Figs. 77 & 78)

1. Drain the primary circuit.

2. Undo the screw securing the microswitch to the

differential valve. Allow the microswitch to rest to one side.

3. Undo the pressure gauge capillary nut and heating flow

pipe nut from the valve.

4. Prise off the bypass connecting clips and disconnect the

heating flow tap. Undo the screws securing the valve to the

boiler bottom panel. Remove the valve.

5. Remove the screws securing the cover from the valve

body. Examine the condition of the diaphragm, spring and

pushrod, replacing as necessary.

6. If required the complete valve assembly can be replaced.

7. Examine the sealing washers and ‘O’ ring on the pipes

and capillary, replacing as necessary.

14.21 Central Heating Differential Valve

Microswitch (Fig. 78)

1. Remove the two wires from the microswitch.

2. Undo the screw securing the microswitch to the valve

body.

3. Reassemble in reverse order.

14.22 Pressure Relief Valve (Fig. 79)

1. Drain the primary circuit.

2. Disconnect the discharge pipe from the valve. Using a

suitable hexagon key undo the grub screw sufficiently to

release the valve.

3. Note the orientation of the valve, rotate it and withdraw

it from the manifold.

4. Fit the new valve and ‘O’ ring seal and set to the

previously noted orientation. Reassemble in reverse order.

Microswitch

Bracket

Diaphragm

Fig. 77

Fig. 78

Pressure Relief Valve

Grub Screw

‘O’ ring seal

Discharge Pipe

Fig. 79