INSTALLATION AND OPERATION INSTRUCTIONS
5-2
SFT 199 TANKLESS WATER HEATER
5.2 ELECTRONIC COMPONENTS
This section details the method for troubleshooting the non-standard electronic
components on the unit.
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 water 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
PURPOSE
LOCATION
S0
NTC 12KΩ
Heat Exchanger
Temperature
Upper Left of Heat
Exchanger
S3
NTC 12KΩ
Domestic Hot Water
DHW Supply Pipe
NTC 12KΩ
Domestic Cold Water
DCW Supply Pipe
S5
NTC 12KΩ
Flue Gas Temperature
Top of rear Flue passage
Table 14: Temperature Sensors
Figure 34: DHW sensor
TEMPERATURE RESISTANCE
TEMPERATURE RESISTANCE
TEMPERATURE RESISTANCE
F / C
Ω - ohm
F / C
Ω - ohm
F / C
Ω - ohm
5F / -15C
76,020
77F / 25C
12,000
149F / 65C
2,752
14F / -10C
58,880
86F / 30C
9,805
158F / 70C
2,337
23F / -5C
45,950
95F / 35C
8,055
167F / 75C
1,994
32F / 0C
36,130
104F / 40C
6,653
176F / 80C
1,707
41F / 5C
28,600
113F / 45C
5,522
185F / 85C
1,467
50F / 10C
22,800
122F / 50C
4,609
194F / 90C
1,266
59F / 15C
18,300
131F / 55C
3,863
203F / 95C
1,096
68F / 20C
14,770
140F / 60C
3,253
212F / 100C
952
Table 15: Temperature Sensor Resistance Values – 12KΩ sensors.
Figure 33: Heat exchanger
temperature sensor
