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Figure 47: Heat exchanger
temperature sensor (Sensor S0)
Figure 48: Water temperature
sensor (Sensor S1)
TEMPERATURE RESISTANCE
F / C
Ω - ohm
5F / -15C
76,020
14F / -10C
58,880
23F / -5C
45,950
32F / 0C
36,130
41F / 5C
28,600
50F / 10C
22,800
59F / 15C
18,300
68F / 20C
14,770
Table 15: Temperature Sensor Resistance Values – 12KΩ sensors.
5-2
SFC BOILER / WATER HEATERS - SFC 199
5.2 ELECTRONIC COMPONENTS
This section details the method for troubleshooting the non-standard electronic
components on the unit, including the electronic water pressure sensor-type
LWCO and the temperature sensors.
5.2.1 Temperature Sensors
The resistance of the temperature sensors varies inversely with temperature. To
test, measure the temperature of the sensed environment and compare with the
value derived from the measurement of the resistance (obtained by connecting a
good quality test meter capable of measuring up to 5,000 KΩ (5,000,000Ω) at the
controller end of the sensor lead).
To obtain a resistance reading, remove power to the unit. For the supply water
and return water temperature sensors, remove the wire leads by disconnecting
their respective Molex connectors. Place multi-meter probes into the sensor's
male Molex connector socket. Do not apply voltage to the sensor as damage
may result.
12KΩ temperature sensors are supplied with the unit. See Table 15 for resistance
values.
SENSOR
TYPE
S0
NTC 12KΩ
S1
NTC 12KΩ
S3
NTC 12KΩ
S7
NTC 10KΩ
S6
NTC 12KΩ
S5
NTC 12KΩ
Table 14: Temperature and Pressure Sensors
TEMPERATURE RESISTANCE
F / C
Ω - ohm
77F / 25C
12,000
86F / 30C
9,805
95F / 35C
8,055
104F / 40C
6,653
113F / 45C
5,522
122F / 50C
4,609
131F / 55C
3,863
140F / 60C
3,253
PURPOSE
Heat Exchanger
Temperature
Heating Supply
Temperature
Domestic Hot Water
Hot Water Tank
Outdoor Sensor
Flue Gas Temperature
Water Pressure
TEMPERATURE RESISTANCE
F / C
149F / 65C
158F / 70C
167F / 75C
176F / 80C
185F / 85C
194F / 90C
203F / 95C
212F / 100C
INSTALLATION AND OPERATION INSTRUCTIONS
LOCATION
Upper Left of Heat
Exchanger
Heating Supply Pipe
DHW Supply Pipe
External Water Heater
Outdoors (North side)
Top of rear Flue passage
Heating Supply Pipe
Ω - ohm
2,752
2,337
1,994
1,707
1,467
1,266
1,096
952
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