Troubleshooting
6.8Error code diagnostics
Part numbers subject to change.
Display | Cause | Solution |
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A2 | Fault in the flue gas limiter (part# | 1. Check for flue gas leakage around the top and |
| 8700400032). | bottom seals of heat exchanger as well as the |
| Note: Old style overheat cutoff fuse | viewing window. Look for any noticeable burn marks |
| (8700400019) has been replaced with this | or warping of the gaskets. If a leak is detected, seals |
| new limiter. | will need replacing. |
|
| 2. Verify that venting meets specifications outlined |
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| in chapter 3.6. Long vent lengths, incorrect venting |
|
| material, venting with more than three elbows, |
|
| blocked vent or combination venting may cause this |
|
| failure. Verify backdraft flapper inside flue gas |
|
| collector is not stuck shut. |
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| 3. Check flue gas limiter wire connectors for |
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| tightness. Clean with pencil eraser if any corrosion |
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| is evident. |
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| 4. Trace wires from flue gas limiter to black |
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| connector. Verify the connection is tight. |
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| 5. If limiter is tripped due to overheating, it must cool |
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| down before error will clear on the control board. |
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|
|
A7 | Hot water temperature sensor fault | 1. Check red wire connections at the hot water |
| (Temperature below 36°F or above 210°F) | temperature sensor. Clean terminals with a pencil |
| (part# 8700400015) | eraser. If badly corroded, replace sensor and wire |
|
| harness. Verify that sensor is firmly clipped on to the |
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| hot water copper pipe. |
|
| 2. Sensor may trip if water temperature drops below |
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| 36°F. Protect heater from freezing condition as any |
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| damage due to freezing conditions is not covered |
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| under warranty. |
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| 3. Clean inlet filter screen per chapter 5.1 and clear |
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| any debris out of showerheads, faucet aerators and |
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| whole house filters. |
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| 4. In areas where water has a high mineral content, |
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| periodic descaling may necessary. See chapter 5.3 |
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| for directions. |
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| 5. Swap sensor with the cold water sensor, keeping |
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| respective wire connections as they are. If the |
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| heater produces an E2 error, replace the sensor. |
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|
|
A9 | Hot water temperature sensor not sensing | 1. Check that the sensor is firmly attached to the |
(Flashing) | expected output temperature. | horizontal section of the hot water pipe. |
| (part# 8700400015) | 2. Clean inlet filter screen per chapter 5.2 and clear |
|
| any debris out of showerheads, faucet aerators and |
|
| whole house filters. |
|
| 3. Verify that venting meets specifications outlined |
|
| in chapter 3.6. Long vent lengths, incorrect venting |
|
| material, venting with more than three elbows, |
|
| blocked vent or combination venting may cause this |
|
| failure. Verify backdraft flapper inside flue gas |
|
| collector is not stuck shut. |
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| 4. Check gas pressure per chapter 3.8*. Low gas |
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| pressure may prevent the heater from reaching |
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| desired output temperature. |
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| 5. Check supply voltage is 120VAC and is properly |
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| grounded. |
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| 6. Possible defective control unit. Call Bosch Water |
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| Heating for further instructions. |
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Table 12
* By installer or service technician only.
36 | 6 720 608 263 |
