Main Heating Main Heat 12, Installation & Service Manual

Page: 64 / 83

The thermistor, safety thermostat, interface PCB and the flow switch can be accessed after removal of the outer case.
15.2 Flow Temperature Thermistor and Safety Thermostat ( Fig. 46 )
1. The procedure is the same for both the thermistor and the safety thermostat.
2. Remove the electrical connections from the sensor.
3. Unscrew the sensor from the pipe.
4. Fit the new thermistor or safety thermostat and reassemble in reverse order.
page 46
15.3 Flowswitch ( Fig. 47 )
1. Drain the boiler (see Section 15.1 paragraph 2 & 3).
2. Remove the two screws on the support bracket.
3. Remove the clip securing the flow pipe to the flowswitch.
4. Disconnect the inline electrical connection.
5. Pull pipe away from flowswitch.
6. Remove the two screws securing the flowswitch to the boiler.
7. Remove the flowswitch.
8. Fit the new flowswitch and reassemble in reverse order.
9. Recommission the boiler and check the inhibitor concentration (see
Section 6.2 and 12.1 ).
Fig. 47
15.4 PCB ( Figs. 48 & 49 )
WARNING: The PCB Control and Fan Assembly are 325 Vdc. Isolate at supply before access.
1. Remove the plastic button cover. Refit them onto the new PCB ( Fig. 48 ).
2. Remove the top right hand securing screw and hinge down the PCB housing and disconnect the electrical connections noting their positions
NOTE: Check the PCB for the presence of input jumpers - see section 10.8. Set the new PCB as the one removed.
3. Lift Control PCB housing out of hinge housing of metal bracket.
4. Fit the new PCB Housing Assembly and reassemble in reverse order.