Figure 10A. Low combustion air switch and pilot gas pressure regulator.

Readjusting low combustion air switch
(Fig. 10A)

1. Make sure that the HEATER CONTROL switch (Fig. 5) is set to OFF.

2. Remove cover from combustion air switch (Fig. 10B).

3. In the control panel unlatch the auxiliary contacts module from the burner motor starter and physically remove it with wires attached (Fig 10B).

4. Pull out the blue plunger on the module and hold it out so as to close its contacts.

5. Restart heater. Limits made light should come on almost immediately.

6. Trip burner circuit breaker. The limits made light should go off within 4 to 5 seconds. If not, readjust as follows: Turn the adjustment screw on the combustion air switch clockwise to shorten the cut-off response time. Turn it counterclockwise to lengthen the cut-off response time.

   
   Figure 10B. Removing auxiliary contacts module and holding plunger out.

Figure 11. Low media level switch.

Checking the low media level switch
(Fig. 11) for proper operation

Before checking the switch for proper operation, confirm that the expansion tank (A, Fig. 9) has an adequate level of thermal fluid. Do this using a measuring stick through the filler opening (B, Fig. 9. If the tank has adequate fluid proceed with checking the switch as follows:

Open the control panel and turn on power to the panel while it is open (Fig. 12). Check for 120 Vac between terminal 50 and neutral. If the voltage is present, the switch is closed and is okay.

Figure 12. Main disconnect circuit breaker with keyed rod.

If no voltage is present, the switch circuit is open and there is a problem with the switch. You can remove the screw-on cover plate from the back of the switch and see if there is a loose wire or an obvious problem with the micro-switch or the linkage that activates the switch. Otherwise, replace the entire switch, including the float portion.

Note: The switch has two parts: a switch housing and a float housing. The float housing protrudes inside the tank and seals the opening so that thermal fluid cannot escape. There is no opening between the float housing and the switch housing. (The float mechanism has a magnet that activates the switch inside the switch housing.) You can open or replace the switch housing without draining the expansion tank. However, you must drain the tank before removing the float housing.