Bosch GWH C 920 ES Reference manual

EA Error Code Troubleshooting
Service Bulletin G3-33
Models: 715ES, C800ES, C920ES, C920ESC, 2400ES, 2700ES, Evolution 500, Integra 500
WARNING: This bulletin includes troubleshooting that
should ONLY be performed by a qualified professional.
Introduction
EA Error code explanation:
The unit could not establish a burner flame signal at start up.
Typically, the unit will make several attempts to establish a flame
before it locks out on an EA error code.
Tools needed:
Phillips head screwdriver
Manometer
Digital Multi-meter
Preparation
Remove cover from heater (see Section 2.2 in Installation Manual).
Troubleshooting
1. Check for spark and flame through heat exchanger site window
(Figure 1, pos. 1) with water flowing. Ignition electodes are
located on inner left side of site window. Record observations
(e.g. Does heater spark several times and lock out? Does it
immediately go to the error code?).
2. Check for correct gas type on label on right side of heater
cover. The heater’s gas type can also be confirmed using the
control board diagnostics feature (see installation manual). If
gas type is incorrect, heater will not operate correctly.
3. Make sure the unit plugged into a clean power supply (e.g.
dedicated socket on a dedicated breaker with no extension
cords, or surge protectors).
Figure 1
C 920 ES/ESC shown - heater design may
vary slightly depending on model
4. Check ground quality on electrical receptacle where appliance
is plugged in.
5. Is the unit installed above 2000 ft elevation? If so, was the unit
calibrated for the elevation? If not, follow the instructions in the
manual for installations at higher elevations.
6. Make sure there are no blockages in the combustion air or
exhaust vent piping. If the unit is drawing combustion air from
inside the building, make sure it has 50 cubic feet per 1000
BTU per hour available. For example, a 175 kBTU heater
requires 8750 cubic feet of air (175000 BTU / 50 ft³ = 8750 ft³).

6
|G3-33 | 715ES, C800ES, C920ES, C920ESC, 2400ES, 2700ES, Evolution 500, Integra 500 Service bulletin
Data subject to change without notice | Printed in the USA | BTC 710002326 A | 03.2013 Bosch Thermotechnology Corp.
Bosch Thermotechnology Corp.
50 Wentworth Avenue
Londonderry, NH 03053
Tel: [phone]
Fax: [phone]
www.bosch-climate.us
7. Check that the P1 and P2 fan speeds are set to the correct
levels in accordance with the vents lengths and altitude. Please
consult the Installation Manual for more information.
WARNING: Steps 8 - 17 include troubleshooting that
should ONLY be performed by a qualified professional.
8. Measure gas pressure under full load with manometer. See
Bulletin Measuring Gas Pressure or Installation Manual for
details. Have gas technician call Bosch Technical Support from
heater to report readings. Record gas pressure readings below:
a) Static: ____”WC
b) Tankless Maximum Power: _______”WC
c) House Full Load: _______”WC
If Full Load or Maximum Power gas pressure is below 3.5“ WC
(NG) or 8.0“ WC (LP), address gas line size or regulated
system pressure to correct.
9. Make sure there is no air in the gas line. Although more
frequent in new installs, this can happen if work is done on the
gas line or after a fuel delivery. If you suspect this, contact a
certified gas technician in your area.
10. Is the unit making any odd grunting or whistling noises? If so, it
may be an indication the fuel/air mixture is incorrect. Fuel/air
mixture can only be adjusted with the use of a combustion gas
analyzer. See Bulletin Measuring & Adjusting CO₂for adjusting
CO₂.
11. If there is no evidence of a heat exchanger leak, inspect for
signs of condensation:
a) Remove the gas valve inspection cover and inspect the area
for any signs of moisture or debris. Make sure the cork
gasket is not damaged and replace it if it shows any signs of
damage. Moisture or rust spots indicate a long term conden-
sation issue that may be causing the error codes.
b) Remove the plastic air supply duct and inspect the fan for
signs of moisture.
c) Remove the heat exchanger site window and using a
flashlight, look for any signs of moisture and debris in the
heat exchanger chamber.
d) Look for any signs that the ceramat burner may be damaged.
Ceramat material that sits above the level of the tray may
indicate damage.
Signs of moisture or damage to the ceramat burner may
require the removal of the heat exchanger for further
inspection and investigation of a potential water leak.
12. Inspect ignition wires and flame sensor wire.
13. Inspect and clean electrodes and flame rod, see Bulletin
Cleaning & Replacing Ignition Group. Verify spacing between
electrodes is no greater than 5.5mm or ¼“. Inspect the ceramic
insulation on electrodes for cracks. Replace electrodes if
damage is present.
14. Measure the voltage to the gas valve on the left hand pair of
wires and the right hand pair of wires. Normally, you will find
24VDC when the unit is running or trying to fire.
15. Measure the resistance of each coil on the gas valve. You should
see 80 Ωon the left pair of pins and 160 Ωon the right pair of
pins.
16. Inspect the wiring harness for defects. Reseat the harness
connections on the control board.
— Check for continuity between ground on the control and
the heater chassis.
If following the procedures did not resolve the problem,
report the troubleshooting results to Bosch Technical
Support. Performing the troubleshooting prior to calling
will speed your call and assist in determining the cause
and solution to the problem.