Why errors appear on Bosch gas boilers and what they mean

Bosch boilers are electronically controlled. By analyzing the readings of several sensors, it quickly responds to changes in operating parameters and optimizes equipment operation on the fly by controlling gas supply, pump and fan speed, flame ignition and other processes. All failures in the operation of units, assemblies and modules, which are parts of the boiler, are analyzed by the built-in self-diagnosis system. When it finds an error, it reports it to the user. Some malfunctions that threaten the safety of others or threaten to break down equipment lead to an instant stop of the boiler or to its refusal to start. But there are also errors in which the boiler continues to work, flashing signal lights to attract attention.

Each manufacturer of heating equipment uses its own code system, developed for a specific model line. In the case of Bosch gas boilers, it is still more difficult, because this manufacturer uses several different systems at once, which are difficult to understand. The fact is that error codes for Bosch boilers of different series and generations are different. Errors can be indicated by combinations of letters and numbers, icons or other symbols, and some models that do not have digital displays signal their malfunctions in other ways (for example, by “winking” the LEDs in a certain sequence).

Below we will look at the main series of Bosch gas boilers and give a decoding of error codes that lead to equipment stopping or malfunctioning.

Error codes for boilers Bosch GAZ 2000 W and Bosch GAZ 6000 W

Bosch wall-mounted gas boilers of the 2000th series ( double-circuit) and the 6000th series ( single-circuit and double-circuit) have the same displays and a common error coding system.

Display of boilers Bosch GAZ 2000 W and Bosch GAZ 6000 W.

When a malfunction occurs during operation, the triangle and wrench icons (both together or separately) appear on the screen, accompanied by a flashing error code. If they do not disappear after pressing and holding the Reset button or turning the boiler off and on, then you need to contact a Bosch heating equipment repair specialist. In some cases, you can, guided by the instructions in the instruction manual, deal with the problem yourself.

This table indicates the main error codes for gas boilers Bosch GAZ 2000 W and Bosch GAZ 6000 W and their decoding.

Display The code Decryption
A7 Incorrect operation of the water temperature sensor.
The temperature sensor or its wire may be defective or damaged.
Ad The tank temperature sensor is not recognized.
Checking the sensor and connecting wire is required.
C1 Low fan speed.
The mains voltage is significantly lower than 230 V, or the flue gas system is not working properly (clogged, blocked or broken).
C4 The pressure switch does not open.
Checking the differential relay, wires and connecting hoses is required.
C6 The pressure switch does not close.
It is required to check the relay and exhaust fan, as well as their wires and plugs.
C7 The fan is not working.
It is necessary to check the fan, as well as its plug and power cable.
CE The filling pressure of the heating system is lower than required.
It is necessary to add water to the system according to the operating instructions and bring the pressure gauge needle to the range recommended by the manufacturer. Also possible: failure of the pressure sensor or its contamination, damage to the expansion tank or an empty air chamber in it.
d7 Incorrect operation of gas fittings.
Inspection of gas fittings and connecting wires should be carried out.
E2 Faulty flow temperature sensor.
Possible damage or short circuit of the sensor, as well as breakage of its wire.
E9 Operation of the water temperature limiter in the boiler.
It is necessary to check the limiter and its wire, the fuse, the circulation pump and the water circuit of the heat exchanger as a whole.
EA The flame was not detected.
The most common error that can have many causes. Problems may lie in the incorrect operation of the gas valve or reducer, low gas pressure in the line, broken wires, clogged chimney or heat exchanger.
The burner is off but a flame is detected.
This error may appear due to contamination of the electrodes, clogging of the chimney or water ingress on the electronic board.
The gas is off, but a flame is detected.
It is required to check the gas fittings, the smoke exhaust system and the electrodes with their wires.
fd Button stuck.
One of the buttons has been pressed for more than 30 seconds. You should check all the buttons, press the Reset button and keep it pressed for 3 seconds.
P Boiler type not defined.
The error occurs when replacing the control unit. You should specify the type and power of the boiler in the service menu.
Fan stage not set.
The fan speed setting of the flue gas exhaust system has not been set.

Some malfunctions and malfunctions do not have their own codes and are not displayed in any way on the digital display of the boiler. These include: noisy operation of the equipment, poor ignition, high Cooling system content in the flue gases, slow heating and insufficient temperature of the hot water at the outlet. In such cases, you should invite the master and diagnose the boiler in order to find the reason for the incorrect operation of the equipment.

Bosch GAZ 3000 W boiler error codes

The series of wall-mounted gas boilers Bosch GAZ 3000 W consists of single-circuit(they have the letters ZS in the marking) and double-circuit(they are indicated by the letters ZW) devices. All variants, regardless of power and class, have the same control panels with liquid crystal displays that serve to display the main operating parameters.

Bosch GAZ 3000 W boiler control panel.

Detecting a problem, the boiler informs the user about this by blinking the LED and showing an error code on the display. The error codes that may appear on the screen of the Bosch GAZ 3000 W gas boiler are shown in the table.

Display The code Decryption
A3 Incorrect operation of the thrust sensor.
The traction control device may be disabled or defective. You should check the sensor and the wire going to it.
A4 Thrust sensor activation.
Insufficient draft in the flue gas removal system. It is necessary to check and clean the flue pipe.
A7 Incorrect operation of the hot water temperature sensor.
Checking the sensor and the wire going to it is required.
AA The temperature in the heating circuit is too high.
Problems may be a sensor malfunction, as well as a pump stalling or insufficient rotation speed. Sometimes this error appears due to the formation of a thick layer of limescale on the heat exchanger.
E0 Low electrical power.
The mains voltage and (or) the frequency of the electric current do not correspond to the standard parameters (230 V, 50 Hz).
E2 Incorrect operation of the heating temperature sensor.
It is necessary to check the sensor and its wire for malfunctions or breaks.
E9 Overheat.
Temperature limiter triggered. It is necessary, adhering to the maintenance instructions, to drain the water from the boiler, remove the air lock in the pump and refill the system with coolant. The restrictor may need to be replaced.
EA The flame was not detected.
There is no flame if the electrodes are dirty or damaged, the gas is shut off or the pressure is too low, there is no power or the wiring is damaged.
F0 Internal failure.
Boiler electronics problems. All contacts and wires should be checked. You may need to diagnose the electronic board or replace it.
F7 Incorrect signal from the flame sensor.
It is necessary to check the sensor and its wire for damage. Sometimes this error appears when moisture gets on the electronic board of the control unit.
FA Incorrect operation of the gas valve.
There was a malfunction in the operation of the gas fittings. Check the gas valve and its wire.

Some of the errors listed in the table are displayed along with a small symbol that looks like the letter "G". By itself, it is not a code, but only indicates that after fixing the problem that led to the error, you should press the fault reset button or restart the boiler.

Bosch GAZ 4000 W boiler error codes

Bosch GAZ 4000 W boilers use an error message system that is not quite traditional for Bosch heating equipment. The fact is that neither single-circuit(with the ZSA marking) nor double-circuit(with the letters ZWA in the name) devices of this series of liquid crystal displays capable of displaying letters and numbers have.

Bosch GAZ 4000 W boiler control panel.

Therefore, to inform users about errors that occurred during the operation of heating equipment, a temperature display screen is used. Having detected a malfunction, the boiler starts blinking LEDs, highlighting certain values of water temperature. According to which numbers are flashing, the user can decipher the boiler's error message.

This table decodes error codes for Bosch GAZ 4000 W boilers that may appear on the temperature display screen.

Display Decryption
Overheating of the heat exchanger.
Temperature limiter triggered. It is necessary to check the temperature sensors and the fuse, check the pressure in the system and (if necessary) bleed air from it.
The flame was not detected.
Make sure that the gas cock is open, the pressure in the gas line is within normal limits, and the boiler is plugged in. Both electrodes and their wires should also be checked.
Activation of the draft sensor (when the burner is running).
The flue system must be checked to ensure that nothing is blocking the evacuation of flue gases. The temperature sensor in the smoke exhaust system and its cable are also subject to verification.
Activation of the draft sensor (when the burner is not working).
It is required to check the flue gas temperature sensor and its wire.
Incorrect operation of the temperature sensor in the supply line.
The sensor and connecting wire should be checked. The error message most often indicates that the sensor is defective and needs to be replaced.
Incorrect operation of the hot water temperature sensor.
An error occurs in double-circuit boilers (marked ZWA) if the temperature sensor does not work, or its wire is damaged.
Incorrect operation of the boiler temperature sensor.
The error appears on the displays of single-circuit boilers (with ZSA marking) if the sensor is not recognized due to a malfunction or damage to the connecting wire.
Incorrect DIP switch setting.
The settings made using the DIP switches do not match the type of equipment and the type of gas used. It is necessary to reconfigure the switches according to the boiler service manual.
Temperature rise too fast.
The flow temperature rises too quickly, the heating mode is automatically switched off for 2 minutes. The error occurs if there is not enough water in the heating system, or the pump does not work. You need to add water or unlock the pump.
Signal from the temperature sensor in the combustion chamber.
The temperature sensor, which is located in the combustion chamber, does not work or is triggered by overheating. It is necessary to check the flue gas exhaust system for clogging, the heat exchanger for contamination, and also make sure that the sensor is in good condition and that its wire is not damaged.

Bosch GAZ 7000 W boiler error codes

The Bosch GAZ 7000 W series is considered the most "advanced" among all traditional gas boilers manufactured by Bosch. Each single-circuit(marked ZSC) or double-circuit(marked ZWC) device from this series has a control panel with a small LCD display under a hinged cover.

Bosch GAZ 7000 W boiler control panel.

In addition to informational messages, the display may show alphabetic and numeric indications of errors that occur when the equipment does not work correctly. The main error codes for Bosch GAZ 7000 W boilers are given in this table.

Display The code Decryption
A7 Incorrect operation of the hot water temperature sensor.
Checking the sensor and the wire with which it is connected is required.
A8 No connection to BUS.
It is necessary to check the connecting wire and regulators.
A9 The temperature sensor is incorrectly installed.
The hot water temperature sensor should be checked. If there is no contact, the sensor is removed and reinstalled using thermal paste.
Ad Boiler sensor not detected.
The temperature sensor on the boiler and the wire leading to it are subject to verification.
b1 Coding plug not found.
It is necessary to check whether the plug is inserted into its socket.
C1 The pressure switch has opened.
It is necessary to inspect the differential relay and check the operation of the exhaust device.
C4 The pressure switch does not open.
Checking the differential relay, wires and connecting hoses is required.
C6 The pressure switch does not close.
The differential pressure switch needs to be checked.
d3 Jumper not found.
There is no jumper on the thermostat terminal block or the plug is not inserted correctly.
d4 Too much temperature difference.
The pressure in the system is not correct. The circulation pump and bypass hose must be checked.
E2 Incorrect operation of the heating temperature sensor.
The sensor and connecting wire should be checked.
E9 Temperature limiter triggered.
The error may be due to a drop in pressure in the system, a malfunction of the temperature sensor, a blown fuse on the control board, a malfunction of the pump or the formation of air pockets inside it.
EA The flame was not detected.
There is no flame due to a closed gas cock or too low line pressure. The error may also appear due to a lack of electricity in the network, damage to the wiring, or a malfunction of the ignition electrode.
F0 Internal failure.
The error appears due to a failure in the electronic subsystems. It is necessary to check the insulation of all wires, as well as inspect the plugs and contacts. It may be necessary to replace the electronic control board for the operation of the boiler.
F7 The boiler is switched off, but a flame is detected.
The device "sees" the flame when the burner is off. Causes are usually contamination of the electrodes or damage to their wires, a blocked flue gas pipe, or water ingress on the electronic board.
FA The gas is off, but a flame is detected.
It is necessary to check whether taps and valves do not let gas in the closed state. The error can also appear due to a malfunction of the ionization electrode or damage to its cable.
fd Button stuck.
The reset button was pressed too long (more than 30 seconds). It should be unlocked and pressed again.
CC Incorrect operation of the outdoor temperature sensor.
Sensor not found or not working. It is required to check the sensor and the cable with which it is connected to the boiler.

Some messages appearing on the indicator board of the Bosch GAZ 7000 W boiler are not error codes. They inform users about special operating modes or equipment settings (for example, that automatic thermal disinfection is currently in progress, or that the key lock is active). A complete list of such signals can be found in the instruction manual for your boiler.

Error codes for boilers Bosch Condens 2000 W and Bosch Condens 2500 W

Representatives of the "younger" (more affordable) lines of Bosch condensing boilers, despite the difference in design, have almost identical systems for informing users about technical failures and malfunctions.

Information displays of boilers Bosch Condens 2000 W (left) and Bosch Condens 2500 W (right).

Error codes for boilers Bosch Condens 2000 W and Bosch Condens 2500 W are shown in the following table.

Display The code Decryption
A2 Operation of the flue gas temperature limiter.
It is required to check the smoke temperature sensor and its wire, the fuse on the printed circuit board, the thermal relay and the operation of the pump. The error can also be associated with clogging of the flue gas exhaust system or the formation of soot on the heat exchanger.
A7 Incorrect operation of the hot water temperature sensor.
The sensor is damaged or defective. You should check the sensor itself and the wire with which it is connected.
A8 No connection to BUS.
Check (if necessary, replace) the connecting cables.
A9 The temperature sensor is incorrectly installed.
The sensor is functioning but not connected well. It is required to remove the sensor and re-install it using thermal paste.
Ad Incorrect operation of the tank temperature sensor.
The temperature sensor on the boiler is damaged or defective. You should check the device and the wire leading to it.
b2 Internal data error.
A reset of all settings and settings to factory values is required. Error codes b4, b5, b6, b7 can mean exactly the same thing.
b3 Activation of the condensate backflow sensor.
It is required to check the sensor (replace if necessary) and the additional heat exchanger (clean if necessary).
C4 The pressure switch does not open.
The differential pressure indicator is in the closed position despite the fan being switched off. Checking the relay, wiring and connecting hoses is required.
C6 The fan is not working.
The fan and the Hall sensor, as well as their cables and plugs, must be checked.
C8 The fan rotates too slowly.
The exhaust fan must be checked and its speed adjusted via the menu according to the length of the flue gas system.
CC Incorrect operation of the outdoor temperature sensor.
Sensor not found or not working. Check the sensor with cable, as well as the diagram of its connection to the connecting terminals.
CE Bosch Condens 2000 W: Temperature rise too fast.
The flow temperature rises too quickly. Check taps and pump. Adjust the pump speed in the pump terminal box.
Bosch Condens 2500 W: System pressure too low.
The water pressure in the heating circuit is too low. Add water to the tank.
d3 Tripping of external switching contact.
Check switch contact and wires. Install a jumper if it is missing.
d7 Incorrect operation of gas fittings.
It is required to check the gas fittings and connecting cables.
E2 Incorrect operation of the heating temperature sensor.
Check the sensor and connecting cable for faults or breaks.
E9 Overheat.
One of the limiters that control the temperature of the boiler block (combustion chamber and heat exchanger) and flue gases has tripped. Following the maintenance instructions, check the limiters and their cables, thermal relays, fuses and pump.
EA The flame was not detected.
The ionization sensor "does not see" the flame. A variety of problems lead to errors: a blocked or blocked gas valve, lack of gas supply or too low pressure in the line, incorrect ratio of gas and air in the combustion chamber, lack of electricity or faulty electrodes and cables, excessive contamination of the heat exchanger with soot or a clogged siphon drain for condensate drain.
F0 Internal failure.
A failure has occurred in the electronic subsystems. Plug-in contacts and plugs, insulation of wires and the condition of the printed circuit board that controls the operation of the boiler should be checked.
F1 Internal data error.
A reset of all settings and settings to factory values is required.
F7 The boiler is switched off, but a flame is detected.
The sensor detects the presence of a flame, despite the fact that the burner is off. The malfunction may consist in contamination of the electrodes, clogging of the chimney, or moisture on the printed circuit board of the boiler control module.
FA The gas is off, but a flame is detected.
The sensor "sees" the flame even though the gas valve is closed. The gas fittings and electrodes with cables should be checked. The problem could also be a clogged condensate siphon or an overgrown chimney.
fd Button stuck.
One of the buttons has been pressed for more than 30 seconds. You should check all the buttons and press Reset, holding it down for about 3 seconds.
PP Boiler type not defined.
The message appears after the control unit has been replaced, if it has not been configured. It is necessary to specify the type and power rating of the boiler through the service menu.
Fan speed not set.
The fan speed is set to "zero" (factory setting). It is necessary to adjust the frequency of its rotation in accordance with the length and configuration of the chimney channels.

Some problems with Bosch condensing gas boilers are not malfunctions, but deviations from the norm. Therefore, they are not detected by the self-diagnosis system and do not have conditional codes. Such malfunctions can only be identified by indirect signs. These include: excessively noisy operation of the pump, slow heating or insufficiently high outlet water temperature, “hard” or uncertain ignition, as well as an increased content of toxic substances in the flue gases. Faced with similar problems, it is better to call a boiler repairman for diagnostics.

In addition to the LCD display, the Bosch Condens 2500 W boiler can “blink” the LED, which is located on the pump control module (it is hidden under the front panel). Thus, the LED indicator, changing color and mode of operation, gives signals about the operation of the pumping unit.

LED signal Decryption
Glows green Normal mode.
The pump is working properly.
Flashing green/red Warning.
The pump is working, but there are problems. There is no danger to the pumping unit.
Blinking red The pump is stopped.
The pump has stopped due to external factors (power surges, overheating or blockage by dirt particles). The node will resume operation when the problem is fixed.
Glows red Stop pump.
The pump unit has completely stopped due to a long-term failure. It is required to check the pump and the electronic module that controls its operation.
Does not glow The pump is not working.
The pump unit does not work due to a lack of voltage or faulty electronics.

Boiler error codes Bosch Condens 7000i W

Modern condensing gas boilers designed for heating and hot water supply are very complex devices. They are “stuffed” to the top with all kinds of sensors and electronic modules that ensure the efficient operation of the equipment in different modes and control all operating parameters. The more parts and assemblies, the more options for malfunctions and failures. Therefore, the latest generations of Bosch condensing boilers use a sophisticated error coding system.

For example, single-circuit and double- circuit boilers Bosch Condens 7000i W, when an error is detected by the self-diagnosis system, two codes are shown on the display at once: the main and the additional.

Display of error codes that do not lead to blocking (left) or stop the operation of the equipment (right) on the display of the Bosch Condens 7000i W boiler.

The main error codes of Bosch Condens 7000i W boilers are indicated by a combination of two letters or numbers (shown on the display instead of the temperature value), and additional ones by a combination of three digits (less often - from a letter and two numbers), they are shown at the bottom of the display. At the same time, an additional code does not always mean an error, most often it is used to indicate normal operating modes.

In addition, for this series of boilers, all errors and notifications are divided into classes, denoted by different letters (they are not displayed on the display, they are used only in technical documentation):

  • O - normal operating mode, not a malfunction;
  • R - a small malfunction that does not entail a shutdown of the boiler;
  • B - a malfunction due to which the boiler is forced to stop until the parameters return to normal;
  • V - a serious malfunction that entails a complete shutdown of the system.

What to do if the Bosch boiler knocks out an error

If your boiler knocks out an error, you should find its decoding in the table corresponding to your equipment model and figure out what it means.

Please note: for other Bosch boilers that are not described in this article, error codes may differ significantly from those indicated in the tables above.

The optimal algorithm of actions when errors are detected by the boiler's built-in self-diagnosis system is to call the Bosch service center, tell the code to the heating equipment maintenance master and follow his instructions. The instruction manual that comes with your boiler usually says what maintenance actions the user can (or should) perform on his own, and which should be done by a certified technician. The latter usually include operations that directly affect the safety of the heating equipment or the reliability of its components and assemblies.