A.O. Smith 100 Series Service Handbook page 18

OPERATIONAL NOTES: When using multiple boilers with the Quad Thermistor Probe staggering each
Boiler's Operating Setpoint by 1° to 3° will achieve greater system energy savings. The Boiler(s) with the
lower Operating Setpoint will reduce their firing rate first and cycle off before the boiler(s) with higher settings.
Setting up a monthly maintenance schedule to rotate which boiler(s) has the higher Operating Setpoint will
also provide a means for lead/lag control which will maintain even wear/operating time for each boiler.
TABLE 3
WATER TEMPERATURE
CELSIUS
3°
21°
38°
49°
55°
60°
71°
82°
16
QUAD THERMISTOR PROBE
FOUR (2 WIRE - COLOR CODED)
TEMPERATURE SENSOR CIRCUITS
FOR USE WITH MULTIPLE BOILERS.
FACTORY EQUIPPED WITH 6 x 1/2 INCH NPT PIPE NIPPLE
TO ACCOMMODATE STORAGE TANK INSULATION THICKNESS.
THIS CAN BE FIELD REPLACED WITH A SHORTER NIPPLE
TO ACCOMMODATE VARIOUS TANKS AND HEATING LOOPS.
FAHRENHEIT
40°
70°
100°
120°
130°
140°
160°
180°
Servicing should only be performed by a Qualified Service Agent
EIGHT WIRE TERMINAL
STRIP FOR CONNECTIONS
MOUNTED INSIDE THE
PROBE COVER
SIDE VIEW
REMOVE 1/8 INCH ALLEN SET SCREW
IN PROBE END TO REPLACE FACTORY
NIPPLE WITH FIELD SUPPLIED NIPPLE.
Figure 9
TEMPERATURE SENSOR
RESISTANCE IN OHMS
26,435
11,974
5,862
3,780
3,066
2,503
1,698
1,177