{"id":8245,"date":"2022-03-21T03:32:45","date_gmt":"2022-03-21T03:32:45","guid":{"rendered":"https:\/\/notsealed.com\/?p=8245"},"modified":"2023-07-31T07:07:51","modified_gmt":"2023-07-31T07:07:51","slug":"diy-bosch-tankless-water-heater-troubleshooting-error-codes-explained","status":"publish","type":"post","link":"https:\/\/notsealed.com\/diy-bosch-tankless-water-heater-troubleshooting-error-codes-explained.html","title":{"rendered":"DIY Bosch Tankless Water Heater Troubleshooting Error Codes Explained."},"content":{"rendered":"\n

There are many different types and sizes of Bosch tankless water heaters on the market. Most have an excellent error displayed to help you diagnose the problem.<\/p>\n\n\n\n

As an electrician, I am often called to diagnose problems with instant hot water units. Also called tankless water heaters. These are very reliable and will tend to last 10-20 years or more.<\/p>\n\n\n\n

I have listed some of the more common error code faults you will come across with some simple repair guides. So read on for our mega Bosch tankless water heater troubleshooting guide.<\/p>\n\n\n\n

Bosch Tankless Water Heater Error Code 10<\/h2>\n\n\n\n
\"Bosch<\/figure>\n\n\n\n

Abnormal combustion. Confirm blockage in either air intake or exhaust. Check the air fan for correct operation.<\/p>\n\n\n\n

Bosch Water Heater Error Code 11<\/h2>\n\n\n\n

No detection of initial flame. The Bosch gas hot water fault code 11 signifies that there is a fault with the unit\u2019s ignition. In this instance, your Bosch hot water heater will not operate and won\u2019t produce hot water until Bosch fault code 11 has been investigated and repaired.<\/p>\n\n\n\n

Bosch Water Heater Error Code 12<\/h2>\n\n\n\n

Flame failure safety device working. Check combustion condition, gas solenoid valve, flame failure safety device, earthing of PCB.<\/p>\n\n\n\n

Bosch Water Heater Error Code 14<\/h2>\n\n\n\n
\"Bosch<\/figure>\n\n\n\n

Overheating protection device activated. Check the wires to the over temp sensor. Check the water pressure and flow rate. Check the exhaust for restrictions. Activates at 184 deg Celsius.<\/p>\n\n\n\n

Bosch Water Heater Error Code 20<\/h2>\n\n\n\n

The remaining flame safety device is activated. Check the cabling.<\/p>\n\n\n\n

Bosch Tankless Water Heater Error Code 29<\/h2>\n\n\n\n

Problem: Something in the unit’s neutralizer is clogged.<\/p>\n\n\n\n

Solution: Try resetting the controller by turning the main power off and on. A flush of the system may be required. You should plan on changing your filler for the condensate capsule at least once per year. Damage to equipment and drains could happen if you don’t replace the unit’s neutralizer regularly.<\/p>\n\n\n\n

I use this tankless hot water flushing kit<\/a> with some white vinegar for my client’s gas hot water units.<\/p>\n\n\n\n

Bosch Tankless Water Heater Error Code 31<\/h2>\n\n\n\n
\"Bosch<\/figure>\n\n\n\n

Abnormal inlet water thermistor. Measure the resistance of the water temperature thermistor. A short circuit is failed. May be hard to find this sensor as it may be behind other electronic parts and pipes.<\/p>\n\n\n\n

Bosch Tankless Water Heater Error Code 32<\/h2>\n\n\n\n
\"Bosch<\/figure>\n\n\n\n

Abnormal outlet water thermistor. Measure the resistance of the water outlet temperature thermistor. A short circuit is failed. Check terminals for corrosion.<\/p>\n\n\n\n

Bosch Water Heater Error Code 61<\/h2>\n\n\n\n
\"Bosch<\/figure>\n\n\n\n

Abnormal combustion fan. Check the fan pulse rate sensor. Also known as an under-speed proximity switch. Check all connections, possible restriction of the fan, or failure of the PCB. The target speed is 500 RPM.<\/p>\n\n\n\n

Bosch Water Heater Error Code 65<\/h2>\n\n\n\n

Abnormal water volume adjusting valve. Confirm the limiter of water adjusting valve. Check connections. Make sure the water inlet volume and pressure are correct. The minimum water flow for correct operation is 2.5L minute. <\/p>\n\n\n\n

Check for scale build-up and flush if necessary. In fact, if your hot water has never been flushed or it has been longer than 5 years between flushing I would get it done. I use this tankless hot water flushing kit from amazon.<\/a> It could save you thousands in repair or replacement hot water plumbing bills.<\/p>\n\n\n\n

Bosch Water Heater Error Code 71<\/h2>\n\n\n\n

The abnormal driving circuit of a gas solenoid valve. Control fault of the driving circuit of the gas solenoid valve. Check for ground faults or faulty PCB.<\/p>\n\n\n\n

Bosch Water Heater Error Code 72<\/h2>\n\n\n\n

Abnormal flame failure safety device circuit (artificial flame.) Measure flame current at extinguish.<\/p>\n\n\n\n

Bosch Water Heater Error Code 73<\/h2>\n\n\n\n

Abnormal PCB setup. Check all dip switches are set correctly to the operating manual for the country\/area. Check gas changing connector and temp changing connector.<\/p>\n\n\n\n

Bosch Water Heater Error Code 760, 76, 0<\/h2>\n\n\n\n
\"YPRM66XB
How to repair Bosch Hot Water Controller<\/figcaption><\/figure>\n\n\n\n

Abnormal remote control communication from the main controller to the gas hot water unit. Check the cable has not been damaged and is free of corrosion on all the terminals. These remote temperature controllers are prone to failure if moisture has found its way onto the internal PCB.<\/p>\n\n\n\n

Disconnect the controller and clean the PCB of corrosion. Replace the Bosch temperature remote controller if required. You can still run the Bosch hot water systems but it will be at a set temperature. Often defaults to 55 deg Celcius. <\/p>\n\n\n\n

\"Bosch<\/figure>\n\n\n\n

You may have a jumper lead attached to the inside of the hot water until you can plug it into the PCB to set the temperature to 60 deg Celsius. I have done a post on how to repair the Bosch hot water wall controller<\/a> if it fails.<\/p>\n\n\n\n

Bosch Error Code 90<\/h2>\n\n\n\n

Problem: Abnormal combustion or low gas supply pressure.<\/p>\n\n\n\n

Solution: Turn the control unit off, turn the hot water tap on, and turn the control unit on. Check the gas supply that it is up to pressure and that it is not isolated.<\/p>\n\n\n\n

Bosch Error Code 92<\/h2>\n\n\n\n

Problem: The water heater\u2019s neutralizer is in need of replacement.<\/p>\n\n\n\n

Solution: Get in touch with a plumber to replace the water heater neutralizer. You should plan on changing your filler for the condensate capsule at least once per year.<\/p>\n\n\n\n

Bosch Error Code 99<\/h2>\n\n\n\n

Problem: Your hot water system has shut down due to abnormal combustion.<\/p>\n\n\n\n

Solution: Isolate the bosch water heater and clean the ignition terminals. Check that the flue is not clogged or restricted. If turning the main power off and on again does not work, you will need to get in contact with a qualified plumber with experience in hot water systems. <\/p>\n\n\n\n

Bosch Tankless Error code A2 – Problem with the flue gas limiter<\/h2>\n\n\n\n

The temperature of the flue gases is too high and is above 230 F. Check for gas leakages or constant flame on the burner. This temperature sensor is located at the top-right corner of the unit.<\/p>\n\n\n\n

Bosch Water Heater Error code A3 \u2013 Wire harness fault <\/h2>\n\n\n\n

Measure the resistance on the wire harness; it must be between 115 and 120 ohms. Also, check the remote control unit if it is attached. <\/p>\n\n\n\n

Bosch Water Heater Error code A4 – Backflow temperature sensor<\/h2>\n\n\n\n

Check the backflow temperature sensor connection for rust or damage. It could also be short-circuited. It is located below the heat exchanger and ignition electrodes. Look for the diagnostic menu 1P and nC code.<\/p>\n\n\n\n

The Flue Safety Device (FSD) has activated indicating the heater is incorrectly flued causing spillage of flue gases into the room, or, the FSD is defective. Disconnect the wiring from the FSD, and measure the resistance. If the resistance is greater than 0.1 ohm, replace the FSD. If the resistance is less than 0.1 ohm, check the exhaust flue hardware on the appliance to ensure it is all on the vertical plane. Pay special attention to the flue cowl which should be an approved model.<\/p>\n\n\n\n

Bosch Tankless Water Heater Error code A7 \u2013 Outlet temperature sensor fault<\/h2>\n\n\n\n

The outlet temperature sensor reacts when the temperature is either below 36 F when the unit is protected from freezing temperatures. Also above 210 F in a case of overheating due to the lime-scale deposits. Check the sensor and wiring for scale, rust, or damage. You might have to flush the unit to remove the mineral scale build-up.<\/p>\n\n\n\n

I use this Kelaro tankless hot water flushing kit<\/a> to descale my client’s hot water systems. It only takes around 1\/2 to 1 hour to descale a tankless hot water system depending on scale build-up. White vinegar works extremely well and is cheap.<\/p>\n\n\n\n

This fault results from the temperature thermistor on the right-hand side of the heat exchanger failing to give a temperature indication. This fault will not stop the heater from operating, but will first display ’00’ on the ICU display before changing to ‘A7’ on the ICU display. Ensure wiring connections to the thermistor. If this does not rectify the fault, test thermistor readings in ohms in conjunction with the thermistor chart to assess correct readings.<\/p>\n\n\n\n

Bosch Water Heater Error code A9 \u2013 Outlet temperature sensor fault<\/h2>\n\n\n\n

This A9 error code is associated with the outlet temperature sensor, but this time, the sensor is not sensing the expected output temperature. This is not an error code; it is a flashing status message that tells you to check; the wiring connection, gas pressure as it might be too low, voltage as it doesn’t meet the required 120\/240 VAC, the unit that might not be properly grounded or the issue with the control board.<\/p>\n\n\n\n

Bosch Water Heater Error code A0<\/h2>\n\n\n\n

This fault results from the temperature thermistor on the right-hand side of the heat exchanger failing to give a temperature indication. This fault will not stop the heater from operating, but will first display ’00’ on the ICU display before changing to ‘A7’ on the ICU display. Ensure wiring connections to the thermistor. If this does not rectify the fault, test thermistor readings in ohms in conjunction with the thermistor chart to assess correct readings<\/p>\n\n\n\n

Temperature \u00b0C<\/td>10<\/td>20<\/td>30<\/td>40<\/td>50<\/td>60<\/td>70<\/td>80<\/td>90<\/td>100<\/td><\/tr>
Resistance K ohms<\/td>22.75<\/td>14.74<\/td>9.78<\/td>6.64<\/td>4.60<\/td>3.25<\/td>2.33<\/td>1.70<\/td>1.26<\/td>0.95<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

Bosch Error Code C6 \u2013 Slow-spinning fan<\/h2>\n\n\n\n
\"Bosch<\/figure>\n\n\n\n

The primary extraction fan spins slowly when the water heater is working. Check the wiring connection on the fan and control board. The voltage must be 120\/240 VAC and the element correctly grounded. Does the venting system meet the code and manufacturer requirements? Ensure that the gas pressure is as required because the low pressure leads to fan rotation problems.<\/p>\n\n\n\n

Bosch Error Code C7 \u2013 Fan rotational speed sensor<\/h2>\n\n\n\n

No signal from the fan’s rotational speed sensor. The sensor might be broken. Check the wire connection on the control board and fan. The voltage needs to be 120\/240 VAC and adequately grounded. Ensure that the fan and control unit is not damaged.<\/p>\n\n\n\n

Bosch Error Code CA \u2013 Excessive water flow<\/h2>\n\n\n\n

Make sure that the water pressure is less than 150 PSI and a flow rate below 10 GPM. Check the wire connections on the water valve and control panel.<\/p>\n\n\n\n

Bosch Error Code E1 \u2013 Extremely high temperature<\/h2>\n\n\n\n

The temperature detected by the outlet temperature sensor is over 185 F. Ensure that the sensor is working correctly, and the wire connections are not loose. Another reason for the high temperature is the sediment build-up, so descaling and flushing will be required. I use this hot water descaling kit.<\/a><\/p>\n\n\n\n

An indication that a water temperature in excess of 85\u00b0C has been detected. This will not cause the appliance to cease operation, however, service attention is required. Verify gas pressure to confirm pressure is not excessive. Also, confirm that the water flow rate did not become insufficient such that the 85\u00b0C settings were exceeded.<\/p>\n\n\n\n

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