DANGER: Risk of electric shock!
▶ Always switch off the electricity supply
to the unit before you remove the cover.
Cold water only – Neon light off
Flow rate is too low
The flow transducer is not
No electricity at the heater or one
of the supplies has failed
One or more of the heating
module thermal cut-outs has
The power supply voltage has
The inlet water temperature is
One of the power supplies is not
Verify the flow rate out of fixture is at or above the minimum activation rate required for the
unit to activate. (Activation rates: WH17 = 0.6 GPM, WH27 = 0.6 GPM).
To test for a plumbing crossover, turn off power supply to the heater. Close installer supplied
cold water shut off valve (if none installed, install before proceeding). Open all hot water taps
supplied by the heater. Wait 5 minutes and check all taps. Any water running is a sign of a
plumbing crossover. Consult a local plumber or service person for help in correcting a
plumbing crossover. To return the heater to service, reinstall cover, open the inlet water
supply to the heater and open all hot water taps. Let all taps run until there is no air coming out
of the fixtures. Shut off all hot water taps. Turn power supply on to the heater. Return heater to
service. (This procedure will prevent the heating elements from burning out).
Turn off the power supply to the heater and remove the cover. Observe if the flow transducer
"spins" when the water is turned on. Please note the flow transducer spins at a high speed and
can appear to be stopped when actually spinning. It is recommended to observe the flow
transducer without water flowing, then turn on a hot water tap while observing the flow
transducer. If the flow transducer is not spinning, remove and flush flow transducer, noting
the Do's and Dont's in section 6 Maintenance. See the technical support section of
www.bosch-climate.us for more detailed instruction on removing the flow transducer.
Have a licensed electrician verify proper wiring and adequate voltage on the terminal block
inside the water heater. See the "Electrical connections" section in section 4.5 Electrical
Connections, of this manual.
Turn off the power to the heater, remove the cover and locate the thermal cutouts on the top of
each heating module. Check for continuity through each cutout. (Less than 0.5 Ohms). A
continuity value greater than 0.5 Ohms indicates that the cutout has tripped or is faulty. A
cutout will only trip in exceptional circumstances and it is essential that the cause is
determined and resolved. Verify the heater's inlet filter screen and all outlets served by the
heater are clear of debris. Ensure the heater is not being fed preheated water. This water
heater is designed for cold water feed only.
Contact Technical Support 800-798-8161 for further instructions.
This is likely an issue with the incoming power supply. Have a qualified electrician measure
voltage on the water heater's terminal block while operating at maximum flow and maximum
temperature setting. The WH17 & WH27 models are rated for 240V and will also operate at
220V or 208V with reduced maximum flow rate.
Verify the heater is sized appropriately for it's geographic location. Turn temperature knob
located on the front of the water all the way clockwise for maximum temperature setting.
Ensure flow rates are within the heater's specifications. Refer to Fig. 11 in section 4.6
Starting Up of the manual. Use of an isolation valve on the cold water inlet to control flow rate
Have a licensed electrician verify adequate voltage on the terminal block inside the water
heater. Verify circuit breakers serving the heater are not tripped. See the "Electrical
connections" section in section 4.5 Electrical Connections of this manual.
Important: If you are unable to perform the tasks listed below,
or need additional assistance please contact your original
Troubleshooting | 19
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