Checking high flue gas stack temperature
With the burner operating, remove cover from the high flue gas temperature switch. Use the flat side of a screwdriver to depress the tiny button on the switch to open its contacts (Fig. 6).

Figure 6. Checking high flue gas stack temperature switch.

The following reactions should occur, indicating that the switch is operating properly:

1. The burner should shut down.

2. The high flue gas stack temperature light on control panel should be the first light to go out.

3. Fireye flame monitor should read 3 TO P INTERLOCK OPEN.

Reset the switch, using the insulated handle of a screwdriver to press the reset button on the switch. This avoids the possibility of electrical shock from the exposed terminals next to the reset button.

Checking circulating pump auxiliary contacts
With the burner operating, trip the circulating pump circuit breaker (Fig. 7).

Figure 7. Burner and circulating pump circuit breakers.

This should cause the auxiliary contacts to open. The following reactions should occur, indicating that the contacts are operating properly:

1. The burner should shut down.

2. The circulating pump auxiliary contacts light on control panel should be the first light to go out.

3. Fireye flame monitor should read 3 TO P INTERLOCK OPEN.

Reset circulating pump circuit breaker.

Checking low media differential pressure switch
This check assumes that the pressure switch was properly set according to instructions in separate Tec-Note prior to purging water from the system.

If the heater has a time delay relay inside the control panel, reset it to zero seconds time delay. With the burner operating, note differential pressure, which is the difference between the values shown on the coil inlet and coil outlet pressure gauges. Also note the setting of the low differential pressure switch. Temporarily turn the dial on the low differential pressure switch counterclockwise until the burner shuts off. The dial should now be set at a value that is 5-10 psi above the pressure difference between the gauges. (Fig. 7.)

The following reactions should occur:

1. The burner should shut down.

2. The low media differential pressure light on control panel should be the first light to go out.

3. Fireye flame monitor should read 3 TO P INTERLOCK OPEN.

Reset dial to previous setting. Also reset time delay relay to previous setting.

Checking high media differential pressure switch
This check assumes that the pressure switch was properly set according to instructions in separate Tec-Note prior to purging water from the system.

If the heater has a time delay relay inside the control panel, reset it to zero seconds time delay. With the burner operating, note differential pressure, which is the difference between the values shown on the coil inlet and coil outlet pressure gauges. Also note the setting of the high differential pressure switch. Temporarily turn the dial on the high differential pressure switch clockwise until the burner shuts off. The dial should now be set at a value that is 5-10 psi below the pressure difference between the gauges. (Fig. 7).

Figure 8. Barksdale pressure differential switch CDPD2H-A80SS

The following reactions should occur:

1. The burner should shut down.

2. The high media differential pressure light on control panel should be the first light to go out.

3. Fireye flame monitor should read 3 TO P INTERLOCK OPEN.

Reset dial to previous setting. Also reset time delay to previous setting.