Download  Print this page

Step 3 - Physical Inspection - Bosch AE12 Troubleshooting Manual

12 kw electric tankless water heater
Hide thumbs


2 |
Troubleshooting Guide | AE12, RP12T, US12
Make sure the heater is not being supplied by preheated or
recirculated water.
Verify that the cold water supply is connected to the INLET
(marked in blue).
Check temperature knob setting (see Figure 2 below):
1. Remove the heater cover.
2. Make sure the temperature spindle is set all the way
Temperature Control Knob
3. Document your fi ndings in the Building and Install
questionnaire on page 5.
Verify flow rate
Using a measured container (a ½ or 1 gallon container
works well), time how long it takes to fi ll it water from
the hot side of a faucet connected to the water heater.
Calculate the fl ow rate by taking the size of the container
and dividing it by the time it took then multiplying the
answer by 60. This will yield a gpm result.
Water collected (gallons)
Time to fi ll (seconds)
Flow rates below 0.6 gpm will not activate the water heater.
Flow rates above 2.0 gpm may cause insuffi ciently warm
Document your fi ndings in the Building and Installation
questionnaire on page 5.
Data subject to change without notice | Printed in the USA | BTC 721002308 A | 09.2013
Figure 2
X 60 = gallons per minute
Checking for plumbing crossovers:
Keep water supply off to the water heater using the
contractor provided isolation valves, isolating the hot water
side of the system.
Do not turn off the water supply to the whole house; only
to the water heater. If you do not have an isolation valve on
the water heater, you cannot perform this test.
Open ALL hot water taps connected to the water heater
and set all fi xtures to hot only.
Allow some time (approx. 5 minutes) for water to stop
running and pipes to drain. If pipes are drained you should
be able to place a hand over end of faucet and feel no
If any water continues to fl ow, you have found a crossover
and one of the following conditions could exist and must
be corrected:
― The most likely cause of this condition is that a mixing
valve has an internal leak allowing cold water to mix with
the hot. While this may not be causing the symptoms
at your water heater, it will certainly affect the ability
of the water heater to reach its maximum stated output
and can cause activation issues and temperature
fl uctuations.
― While unlikely, a cold water pipe could be connected to
a hot water pipe. If you have had some plumbing work
done recently and the symptoms coincide with the work
done, you may want to contact the person that did the
Close all fi xtures and reopen water supply to the water
Document your fi ndings in the Building and Installation
questionnaire on page 5.
Step 3 – Physical inspection
Visual Inspection
Thoroughly inspect the water heater's internal
components. Note the following:
― Burn or scorch marks on the PCB (Printed Circuit Board)
― Any signs of melted or damaged wires
― Cracks in plastic components
― Alignment of components
― Screw tightness
Document your fi ndings in the Water Heater questionnaire
on page 6.
Bosch Thermotechnology Corp.



  Related Manuals for Bosch AE12

This manual is also suitable for: