Bosch WH27 - Page 4

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WH17, WH27, WH36 AE115, AE125, (FD108 and higher)
Data subject to change without notice | Printed in the USA | BTC 722002309 B | 05.2014
Bosch Thermotechnology Corp.
Step 5 – Troubleshoot the element assemblies
 Verify that circuit breakers are off and there is no voltage at the
unit.
 Measure resistance of element assemblies (Fig. 7):
— For 17kW models:
1. Using a 200 ohm range on a digital multi-meter, test all the
elements on left heating module.
― Outer to Outer (Brown wire with the black insulation
to left side of the TCO)
― Inner to Inner (Black wire with the black insulation to
left side of the TCO)
2. Using a 200 ohm range on a digital multi-meter, test all the
elements on left heating module.
― Outer to Outer (Brown wire with the black insulation
to left side of the TCO)
― Inner to Inner (Blue wire with the black insulation to
left side of the TCO)
— For 27kW and 36kW models:
1. Using a 200 ohm range on a digital multi-meter, test all the
elements on left heating module.
― Outer to Outer (Brown wire with the black insulation
to the bottom left side of the TCO)
― Inner to Inner (Blue wire with the black insulation to
the bottom left side of the TCO)
― Middle to Middle (Gray wire with the black insulation to
top left side of the TCO)
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Rear of Heater
Front of Heater
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Rear of Heater
Front of Heater
Center Module Top View
(36kW model only)
RIGHT MODULE Top View
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Rear of Heater
Front of Heater
LEFT MODULE Top View
NOTE: on 17kW models, there is no middle element
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N
OTE: on 17kW models
,
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Figure 6
2. Using a 200 ohm range on a digital multi-meter, test all the
elements on right heating module.
― Outer to Outer (Brown wire with the black insulation
to the bottom left side of the TCO)
― Inner to Inner (Black wire with the black insulation to
the bottom left side of the TCO)
― Middle to Middle (Gray wire with the black insulation to
top left side of the TCO)
— 36kW model only:
1. Using a 200 ohm range on a digital multi-meter, test all the
elements on center heating module.
― Outer to Outer (Brown wire with the black insulation
to the bottom left side of the TCO)
― Inner to Inner (White wire with the black insulation to
the bottom left side of the TCO)
― Middle to Middle (Gray wire with the black insulation to
top left side of the TCO)
— All Models:
1. Using the 20 Mohm (Mega ohm) range on a digital multi-
meter, test each element tip to ground.
2. Record all readings along with where you encountered
them.
3. Using the 200 ohm range on a digital multi-meter, test the
resistances across the terminals of the TCOs (Thermal Cut
Outs).
 Record your results in the Water Heater questionnaire.