Bosch AE12 Troubleshooting Manual page 4

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Troubleshooting Guide | AE12, RP12T, US12
Check the resistance of the elements.

1. Ensure that the power to the unit is turned off.
2. Set your multimeter to an appropriate setting to be able to
test for resistance in the 10 ohms range.
3. Place the red probe on the steel bar as shown in Figure 6
below and keep it there.
4. Place the black probe down inside the two white plug
connectors shown in Figure 7, one after the other, and
write down the resistance readings of each. Ensure that
you make good contact with the probes to improve the
accuracy of your test result.
5. Document your fi ndings in the Water Heater questionnaire,
page 6.
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Data subject to change without notice | Printed in the USA | BTC 721002308 A | 09.2013
Check to see if either element is grounded to the water tubing.

1. Ensure power supply to the unit is off.
2. Set your multimeter to Mohms (2000K, 2M, or 20M).
3. Place one multimeter probe on the common steel bar that
joins the two element terminals together (Fig. 6) and touch
the other probe to the copper water tubing to see if you
have any continuity or resistance there.
4. Document your fi ndings in the Water Heater questionnaire,
page 6.
Figure 6
Step 5 – Verify the power supply
The power will need to be turned on for this test, please use

caution. Check the power supply using an appropriate scale.
1. Measure the incoming voltage across L1 and L2 terminals
(see Fig. 8) to be sure the unit is receiving 240 VAC.
Figure 7
2. Record your results in the Water Heater questionnaire on
page 6.
L1 and L2 Incoming power terminals
Bosch Thermotechnology Corp.
Figure 8