These Bosch hot water heaters are fitted with self diagnostics electronics. When a fault occurs, the heater will shut down and the fault with a pair of digits will be displayed on the display screen. Refer to the following table for probable cause and suggested remedy.
Fault Condition : Something in the units’ neutraliser is clogged.
Item to check : Try resetting the controller by turning the main power off and on.
Fault Condition : Abnormal combustion or law gas supply pressure.
Item to check : Turn the control unit off, turn the hot water tap on and turn the control unit on.
Fault Condition : The water heater’s neutraliser is in need of replacement.
Item to check : Get in touch with a plumber to replace the neutraliser.
Fault Condition : Your hot water system has shut down due to abnormal combustion.
Item to check : 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.
Fault Condition : There is a problem with your heaters hot and cold sensors.
Item to check : Turn the unit off, turn on the hot water tap and turn the power back on. Replace the sensor and/or wire is problem persists.
Fault Condition : The temperature within the hot water unit is hotter than average.
Item to check : Call a qualified plumber.
Fault Condition : Fault in the flue gas limiter
Item to check : Call a qualified plumber
Fault Condition : Wire harness defect.
Item to check : Call a qualified plumber
Fault Condition : The air temperature sensor is faulty.
Item to check : Call a qualified plumber
Fault Condition : Condensing unit flue temperature sensor disconnected or damaged
Item to check : Replace the sensor and/or wire connections with the help of a qualified plumber
Fault Condition : Inlet cold water temperature sensor disconnected or damaged.
Item to check : Replace the sensor and/or wire connections with the help of a qualified plumber
Fault Condition : The water temperature sensor is faulty.
Item to check : Replace the sensor and/or wire connections with the help of a qualified plumber
Fault Condition : Outlet hot water temperature sensor disconnected or damaged.
Item to check : Replace the sensor and/or wire connections with the help of a qualified plumber
Fault Condition : No hot water or inconsistent temperatures.
Item to check : Turn the power off, turn on the hot water and turn the power back on. If this doesn’t work, check the gas supply pressure with the help of a qualified plumber.
Fault Condition : Condensing unit flue gases temperature too hot.
Item to check : Check flue gas temperature sensor, water inlet temperature sensor, and descale the tankless water heater with the help of a qualified plumber.
Fault Condition : Flue blockage detected during startup
Item to check : Reset error (press and hold on/off button for 3 seconds). If issue persists, Check air openings and exhaust opening for obstructions and reset. Check if flue length is according to manual specification and reset the system to clear error. Check if the air filter is dirty or clogged, replace it if needed. Perform gas and air tuning according to manual, or with the help of a qualified plumber.
Fault Condition : Fan calibration triggered due to missed ignitions
Item to check : Check gas inlet pressure and perform gas and air tuning with the help of a qualified plumber.
Fault Condition : Successive fan calibration with similar learned values.
Item to check : Check gas inlet pressure and perform gas and air tuning with the help of a qualified plumber.
Fault Condition : Little to no air flow meaning that the heater cannot start up.
Item to check : Turn the hot water tap on to its full capability and then turn it off. Then turn the system on and off.
Fault Condition : Flow sensor does not detect water recirculation.
Item to check : Check pump and connections, then check recirculation circuit for any blockage.
Fault Condition : Bypass water valve disconnected or damaged.
Item to check : Check bypass water valve wire connections, if error continues, Replace the bypass water valve and/or wire connections with the help of a qualified plumber.
Fault Condition : Primary fan rotation too low
Item to check : Check gas pressure. Low gas pressure may cause the fan to change its speed to meet desired temperature. Possible defective control unit call a qualified plumber to fix the issue.
Fault Condition : A faulty fan, only cold water will be able to be used.
Item to check : Replace the fan and/or wire connections with the help of a qualified plumber.
Fault Condition : Main water valve disconnected or damaged.
Item to check : Check main water valve wire connections, if error continues, Replace the main water valve and/or wire connections with the help of a qualified plumber.
Fault Condition : Barometric pressure sensor damaged.
Item to check : Reset error, if problem persists, replace electronic control unit (ECU) with the help of a qualified technician.
Fault Condition : Water Flow Fault
Item to check : Disconnect power supply cord and check wire connections on water valve and the two connectors on the control board. Excessive water pressure/flow, call a qualified plumber to fix the issue.
Fault Condition : Excessive flue blockage detected
Item to check : Excessive flue blockage detected during operation due to excessive pressure on the siphon. Check exhaust pipes and terminals for obstructions and reset the error.
Fault Condition : Excessive flue blockage detected during operation due to insufficient combustion air.
Item to check : Check air intake and exhaust pipes and terminals for obstructions and reset the error.
Fault Condition : Electronic control unit internal error.
Item to check : Reset error, if problem persists, replace electronic control unit (ECU) with the help of a qualified technician.
Fault Condition : Hot water temperature above 90°C
Item to check : Disconnect the appliance and purge hydraulic circuit to remove air, if problem persists, reduce set point temperature to minimise temperature instabilities with the help of a qualified technician.
Fault Condition : Cold water temperature sensor fault
Item to check : Check connector on wires coming from top of water valve for a secure connection, Sensor may trip if water temperature drops below 2°C. Protect heater from freezing conditions.
Fault Condition : Exhaust temperature sensor
Item to check : Descale the tankless system, reset error, if problem persists, check sensor resistance and replace the sensor with the help of a qualified technician.
Fault Condition : Backflow Temperature Sensor
Item to check : Check inlet/outlet vent pipes, check if secondary fan connections are disconnected, check venting specifications are met. Long vent lengths, venting with more than three elbows, blocked vent or combination venting may cause this failure.
Fault Condition : Condensing unit flue gases temperature too hot.
Item to check : Descale the tankless system, reset error, if problem persists, check sensor resistance and replace the sensor with the help of a qualified technician.
Fault Condition : Electronic control unit internal error.
Item to check : Reset error, if problem persists, replace electronic control unit (ECU) with the help of a qualified technician.
Fault Condition : Error during ionization test
Item to check : Error during ionization test. Electronic control unit internal error, replace electronic control unit (ECU) with the help of a qualified technician.
Fault Condition : Thermal fuse broken
Item to check : Replace thermal fuse with the help of a qualified technician.
Fault Condition : Ignition failure.
Item to check : Check gas inlet pressure and perform gas and air tuning with the help of a qualified plumber.
Fault Condition : Electronic control unit internal error
Item to check : Reset error, if problem persists, replace electronic control unit (ECU) with the help of a qualified technician.
Fault Condition : Flame lost during operation.
Item to check : Check gas inlet pressure and perform gas and air tuning with the help of a qualified plumber.
Fault Condition : Gas valve modulation solenoid disconnected
Item to check : Check gas valve wire connection, if problem persists, replace the gas valve and/or wire connections and or electronic control unit (ECU). For gas valve replacement, perform gas and air tuning with the help of a qualified technician.
Fault Condition : Wrong gas connected.
Item to check : Wrong gas connected (LPG instead of Natural Gas) for current appliance configuration, check gas type.
Fault Condition : Electronic control unit internal error
Item to check : Reset error, if problem persists, replace electronic control unit (ECU) with the help of a qualified technician.
Fault Condition : Ionization error at standby
Item to check : Loose connection to the flame ionization rod. Verify that the thinner wire leading from the control unit is securely connected to the set of electrodeslocated on the lower front of the heat exchanger, flame ionization rod or control unit may be damaged, call a qualified technician to rectify the issue.
