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TWH-G2-07 | 2400E, 2400EO, 250SX, 250SXO, 635ES, 635ESO
Service bulletin
Control board diagnostics
Introduction
Control boards having software versions 3003 and newer are
equipped with full diagnostic features. Older model control
boards are not capable of running software version 3003 and
newer. Contact Bosch Water Heating at 1-800-642-3111 with
questions.
Tools needed:
None
Determining diagnostic mode availability
1. Turn on/off switch on water heater to off (O) position then back
to the on (I) position. Quickly observe the fi rst set of letters on
the LCD display of control unit. If the heater displays the letters
"SU", then diagnostics are not available with this software
version. If the heater displays the letters "AF", then diagnostics
are available and you may proceed to the next step.
Accessing diagnostic mode
1. Turn on/off switch on water heater back to off (O) position.
2. Press and hold the program (P) button (M on older models)
while turning the on/off switch to the on (I) position. The
display will cycle through a start-up procedure including soft-
ware version.
3. Release the 'P' button when '188' appears on the display. The
display should read 'P2' when the program button is released. If
not, repeat process.
4. Press the '+' button on the control panel until the display reads
'P4'. You are now in the diagnostic mode of the control board.
5. When the display reads 'P4', press the 'P' button once again and
the display should read 'E'.
6. Use the '+' and '-' button on the control board to cycle through
different diagnostic modes available.
NOTE: Each diagnostic mode that appears on the LCD display
will have a number on the left and a letter on the right. If the
letter on the right is an upper case P, then refer to Software
Version 3003 of the diagnostics table on the back page. If the
letter on the right is a lower case "d", then refer to Software
Version 3005 of the diagnostics table on the back page.
7. Once in the selected diagnostic mode of your choice, press the
'P' button to display the diagnostic information.
EXAMPLE(using software version 3005): To read the fl ow rate in
gallons/minute while the unit is fl owing water, cycle to the '3d'
mode and press the 'M' button. A reading of 25 on the display
would indicate the heater is reading a fl ow rate of 2.5 gallons/
minute.
8. Once the information is obtained, press the 'P' button again to
return to the diagnostic mode menu and scroll to additional
diagnostic information.
9. To exit the diagnostic mode of the heater, use the '+' or '-'
button until the display reads 'E'.
10. Press the 'P' button once again and the display should read P4.
11. Turn the on/off switch off (O) and back on (I) again to return
heater to normal function.
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