Series AA250
Page 21
LT252 Oct 2019
Remove these two (2) screws
to access the back of the
sensor
HIGH LIMIT SWITCH
WARNING
Burn Hazard
•
Do not operate the heater with the high limit switch bypassed
•
Operating the heater with the high limit switch bypassed may lead to overheating, possibly resulting in a fire,
with subsequent damage to the heater, to the building, or loss of livestock
The heater uses a high limit switch for the purpose of overheat protection. The high limit switch is located on the
combustion chamber above the burner, and is connected between the ignition control and the gas control valve.
The switch is normally closed, and will open the switch contacts if an overheat condition occurs. The high limit
switch should be tested a minimum of once per year when the heater is given a thorough cleaning.
1. Remove the switch. Apply a small flame only to the sensing portion on the back of the switch. Do not melt
the plastic housing of the switch when conducting this test.
2. Within a minute, you should hear a pop coming from the switch, which indicates the contacts of the switch
have opened. Check for lack of electrical continuity across the switch terminals to verify contacts have
opened.
Figure 12 – High limit switch
