Models: 2400ES, 2700ES, 715ES, C800ES, C920ES, C920ESC, Integra 500, Evolution 500

A4 - E4 Error Code Troubleshooting

Service Bulletin G3-16

IntroductionThe following procedures are for gathering information to assist Bosch Tech Support in determining the cause and solution to the problem. Unplug power cord and remove outer and inner covers from heater (refer to Installation Manual).

Error code explanation:A4 error code explanation: Backflow temperature sensor faultE4 error code explanation: Backflow temperature sensor over 309° F.

Tools needed: Phillips head screwdriver Multimeter

A4 troubleshooting procedure

1. Check connection between backflow temperature sensor and wiring harness. Black wires and connector should be plugged into white connector with green wires (Figure 1).

white connector

black connector

whiteconnector

blackconnector

Figure 1

2. Remove control unit from heater and reseat wire harness connector on circuit board:

a. Remove 3 screws attaching control unit to heater (Fig.2, pos.1).b. Turn control unit over (Fig.2, pos.2).c. Remove 6 screws on rear cover of control unit (Fig.2, pos.3).

control unit frontcontrol unit front

Figure 2

d. Remove rear cover.e. Locate wire connectors on edge of circuit board. f. Remove and reinstall connectors onto edge of board to

improve the electrical connection (Fig.3, pos.1,2,3)

Figure 3

1 2 3

4 | G3-16 | 2400ES, 2700ES, 715ES, C800ES, C920ES, C920ESC, Integra 500, Evolution 500 Service bulletin

Data subject to change without notice | Printed in the USA | BTC 710002322 A | 08.2009 Bosch Thermotechnology Corp.

Bosch Thermotechnology Corp.50 Wentworth AvenueLondonderry, NH 03053

Tel: 1-800-642-3111Fax: 1-603-584-1681www.boschhotwater.com

E4 troubleshooting procedure 1. Check intake, exhaust vent and terminations for:

a. Blockage or restriction.b. Excess vent length over maximum. See manual for correct

vent requirements.c. More than 4 90 degree elbows plus termination in each vent.

2. When heater is in operation with burners fired and covers off, measure voltage between 2 black wires on secondary fan (Fig.4, pos.1).

CAUTION! Keep hands and tools away from spinning blades on right side of fan.

Figure 4

1

a. If there is no voltage present, wiring may be faulty: Ensure that 3 wire connections to fan are secure.

3. If voltage is present but fan is noisy or does not spin: Turn off power to heater and check the following:a. Ensure that fan is securely mounted with 2 screws at top of housing to underside of burner. (Fig. 5, pos. 1)b. Check fan motor mounting bushings for damage. If damaged, replace fan. (Fig. 5, pos. 2). Note: 3rd bushing not visible in Figure 5. It is located toward the rear of the fan.

c. Check fan blades for free spinning:• If debris is blocking blades in housing, remove fan and

debris, reinstall fan.• If blades hit housing, fan motor bushings may be

damaged and fan may need to be replaced.

1

2

Secondary fan

base of burners

1

2

Secondary fan

base of burners

Figure 5