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1 0 | TWH-G2-05 | 2400E, 2400EO, 635ES, 635ESO, 250SX, 250SXO
Testing temperature sensors
1. Turn the on/off switch on the water heater to off. Display should
be blank.
2. Remove the wire spade connections on both temperature
sensors.
3. Remove the hot water temperature sensor from the outlet pipe
and place this directly adjacent to the cold water sensor on the
inlet pipe inside the water heater. Make sure that both sensors
are seated fi rmly on the copper pipe.
4. Turn on a hot water fi xture such as a sink and allow water to run
steadily through the water heater for 5 minutes. Using a thermo-
meter, measure the temperature of the water fl owing out of this
tap. Continue running water and go back to the water heater.
5. Using a multi-meter set on kilo-ohms (kΩ), measure the
resistance between the two connections of each sensor and
record readings.
6. Refer to the table below for resistance readings in accordance
with water temperature readings. NOTE: Readings are approxi-
mate. If readings are inconsistent between sensors and/or do
not match approximate readings, replace the sensor with impro-
per readings. If sensor readings are accurate according to the
table but still give inconsistent temps or an error code, contact
Bosch Water Heating Technical Support at 800-642-3111.
Temperature sensor readings
Temperature
32 °F
55 °F
65 °F
100 °F
120 °F
140 °F
Data subject to change without notice | Printed in the USA | 1.2007
Approximate resistance reading
40 kΩ
22.5 kΩ
13.5 kΩ
7.5 kΩ
4.5 kΩ
3.5 kΩ
Service bulletin
BBT North America Corporation
Bosch Group
Bosch Water Heating
340 Mad River Park
Waitsfi eld, VT 05673
Telephone 800-642-3111
Fax (802) 496-6924
techsupport@boschhotwater.com
Bosch Water Heating
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