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Page 24
Figure 35. Testing the manual reset hi-limit switch.
fire. If the water flow is too low, the switch remains
open and prevents the heater from firing regardless of
the temperature control setting.
The flow switch is factory mounted and wired.
Never attempt to repair the flow switch. If the flow
switch is found to be defective, replace the flow
switch. To test the flow switch:
1.
Remove cap from flow switch.
2.
Touch a voltmeter lead to each terminal of the
flow switch.
3.
If the voltmeter reads voltage at each of the
terminals, the switch is good.
4.
If there is no voltage at one terminal, it indicates
an open switch. Replace the flow switch.
5B-6. Testing the Fusible Link
(flame roll-out switch)
The fusible link is a thermally fusible element
which shuts down the heater if it detects excessive
temperatures inside the heater flue collector
compartment. To test the fusible link (flame roll-out
switch, if installed):
1.
Remove the electrical wiring from the fuses and
check across each fuse's terminals with a
continuity or ohm meter.
2.
Touch the voltmeter lead to the lower terminal on
the terminal block (see Figure 36).
3.
If the voltmeter reads voltage, the safety fuse and
the fusible link are good.
4.
Replace the fuse when an open circuit is
detected. An open fuse indicates overheating in
the flue collector or compartment.
5.
Check for leaks of the flue collector, vent pipe,
gaskets, and all connections.
6.
Check the flue pipe for blockage.
5B-7. Testing the Fuse
To test the fuse:
1.
Clip a lead of the voltmeter to the grounding
terminal.
2.
Touch the other voltmeter lead to the 24VAC
terminal on the ignition control.
3.
If there is no voltage, replace the fuse. A blown
fuse is usually an indication of a short in the
24VAC circuit. It is important that the cause of
the short be found and repaired. Do not jumper
or bypass the fuse.
5B-8. Testing the Ignition Control
(for spark ignition)
The ignition control and igniter operate on 120V
power. Keep this in mind while servicing the heater,
and take care to avoid electrical shock.
The ignition control provides power to the
igniter, opens the gas valve when there is a call for
heat, and senses when a flame is established. To test
the ignition control for spark ignition:
1.
Clip one lead from the voltmeter to the yellow
wire terminal on the transformer.
Figure 36. Testing the fusible link.
Caution
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