Bosch gas boiler errors: decipher common errors and resolve them

Are you familiar with a situation where you see an error code and you don’t even know what it means? Perhaps you always lose the instructions for household appliances, and searching for information on the network does not give anything. In this article, we indicated the errors of Bosch gas boilers, their decryption and the necessary steps to eliminate. It will not hurt you to remember about it if you also have a Bosch boiler and an error suddenly lights up on its display. It will be good if the article helps you at the right time.

There is usually little space on the displays of boilers, so the problem has to be transmitted with a short cipher. Thanks to our material, you will be guided in all the main types of errors. You will not be afraid of the simple letters and numbers that appear on the boiler.

Varieties of errors and methods for eliminating them depend on the principle of operation of the gas boiler, its internal structure. In the case of Bosch devices, there are not so many error codes in general, and most of them have been unified for all modern models of this brand.

Bosch boiler error categories

Bosch produces boilers of different capacities for heating running water, heating homes and underfloor heating systems. Series Devices Eurostar made under a common brand Junkers bosch.

Boilers Bosch and Bosch Eurostar give errors that indicate a particular problem or its cause. It is necessary to distinguish error codes for devices from different model ranges under these brands, they sometimes differ. Failures themselves do not yet indicate a hardware problem.

Bosch Gaz 6000 W WBN 6000-24C RN boiler control panel: this device was adapted to Russian conditions and this is the first domestic boiler under the international brand manufactured in Russia

Popular series and models:

• Bosch Gaz 7000 W ZSC: 24-3 MFA, 35-3 MFA, 24-3 MFK;
• Bosch Gaz 7000 W ZWC: 24-3 MFA, 28-3 MFA, 35-3 MFA, 24-3 MFK, 28-3 MFK;
• Bosch Gaz 6000 W WBN 6000-24C RN;
• Bosch Eurostar ZWE: 24-4 MFA, 28-4 MFA, 24-4 MFK;
• Bosch Eurostar ZSE: 24-4 MFA, 24-4 MFK.

In case of an error, you need to find out the reason from its decryption, examine a separate part of the device and determine by its condition that the notification did not appear by chance.In the worst case, owners are waiting for repairs, replacement parts or the entire device. It should be remembered that ordinary consumers should not touch parts through which gas enters the boiler. Most errors pop up not after breakdowns, but because of working conditions.

Problems in the operation of boilers do not always appear as errors. Difficulties also arise with the temperature of the supplied water. The liquid sometimes gets too cold or hot. Only a master of gas boilers will help in this case. If the device is new, then the problem may lie in the wrong type of gas.

Due to unregulated circulation pump sometimes there are inconveniences like a long heating time and the noise of the water stream. Constant problems with starting the boiler indicate a low gas pressure, clogging of the discharge paths or a violation of the links in the electrical circuit.

Circulation pump for Bosch gas boiler: this part of the device accelerates the heated fluid through the heating system, so that the coolant cools more slowly, the second heating cycle becomes shorter, and the next ones approximately correspond to the second

These are only common problems. Errors in the main categories:

• A: A2, A3, A4, A6, A7, A8, A9, AC, Ad;
• C: C1, C3, C4, C6, C7, CC, CE;
• d: d1, d3, d4, d5, d7;
• E: E0, E2, E9, EA, ER;
• F: F0, F7, FA, Fd.

Errors also pop up due to the fact that the wizard did not install individual nodes or did it incorrectly. Often there is a problem with the fan stage.

Category # 1 - Error Codes on A

A2 - on the combustion chamber there is an emission of flue (exhaust, exhaust) gases. All you need is to see if dirt has accumulated on the heat exchanger and remove it. This is usually enough.

A3 - the system does not see the NTC-sensor for the temperature of the exhaust gases. On Bosch Eurostar ZWE 24-4 MFK and Bosch Eurostar ZSE 24-4 MFK boilers, an error warns of a shorted or damaged traction control fuse. In both cases, check the condition of the connecting (contact) cable and the NTC sensor.

A4 - exhaust gas discharge on the flow guard. Inspect the flue gas exhaust manifold.

A6 - The temperature sensor of the combustion chamber is not detected. In this case, the contact wire and the temperature sensor of the combustion chamber are checked for damage.

A7 - malfunction of the NTC hot water temperature meter. A short circuit or break could occur. Find out what with the NTC sensor and its wire, replace if necessary.

A8 - no connection to e-BUS bus. You need to inspect the knobs-regulators and connecting cable.

A9 - Incorrect installation of the hot water temperature sensor. Check the installation location. Remove the sensor, in which case, reinstall and add thermal paste.

The hot water temperature sensor is installed with a wrench at 15, in the photo - a device for Bosch and Junkers

AC - module connection error - for Bosch Gaz 7000 W ZWC 24-3 MFK, ZWC 28-3 MFK, ZSC 24-3 MFK boilers. Make sure that the Bosch module or remote control connected to the gas boiler is working properly, as well as the connection itself and the external temperature sensor. Troubleshoot.

In Bosch Eurostar devices, an AC error indicates a problem with the interaction of the connected module and Heatronic. Check the wire between them.

Ad - the boiler temperature sensor cannot be recognized - in Bosch Gaz 7000 W ZSC 24-3 MFA, ZSC 35-3 MFA, ZWC 24-3 MFA, ZWC 28-3 MFA, ZWC 35-3 MFA, Bosch Gaz 6000 W WBN 6000- devices 24C RN, Bosch Gaz 7000 W ZSC 24-3 MFK, ZWC 24-3 MFK, ZWC 28-3 MFK.

Bosch Eurostar ZWE 24-4 MFA, ZWE 28-4 MFA, ZSE 24-4 MFA, ZWE 24-4 MFK, ZSE 24-4 MFK Ad error indicates damage to the tank’s NTC temperature sensor. In both situations, check the contact wire and the temperature meter itself.

Category # 2 - C Breakdowns

C1 - opening of the differential pressure switch during operation. Inspect relays, connecting pipes, and a fume hood. In Bosch Gaz 6000 W WBN 6000-24C RN boilers, a malfunction with code C1 means a low fan speed. In this case, check the mains voltage and the flue gas exhaust channels. The latter sometimes have to be cleaned and repaired.

C3 - corresponds to the above error A2.

The differential relay operates in 2 modes: at normal pressure, the diaphragm does not change position, and if the system malfunctions, the membrane bends and all heating equipment stops working

C4 - the differential relay does not open when the fan is idle. You need to see what happened with the relay.

There are two ways out of the situation:

1. Remove the relay and blow out the tubes that go from it.
2. Determine with a multimeter whether there is a short circuit, open circuit, mismatch with the nominal resistance. Replace relay if necessary.

C6 - the pressure switch does not close. Look at the device itself and the flue gas elimination system. Remove the relay and remove condensation from the tubes with a hairdryer. Test for open and short. Remove excess from the chimney. It can be frost, ice, etc.

C7 - the fan does not work. Check this device, its wire and plug.

CC - no external temperature sensor found. In Bosch Eurostar series boilers, the CC code indicates the breakage of this temperature sensor. Look for damage and possible breakage of the meter and contact cable.

CE - The pressure in the heating system is too low. If the pressure gauge points to the red zone, add water through the make-up valve. If the gauge needle is in the green area, then there is a problem with it. Sometimes a problem occurs in the membrane or microswitch.

Category # 3 - faults on d

d1 - there is no response from the LSM sensor (safety position sensor). Look for a problem in the wires coming from the LSM. Inspect the floor heating limiter.

d3 - there is no jumper 161 on ST8. Find out if there is a jumper. If so, also inspect the external stop and insert the plug correctly.

The scheme of operation of the controller-limiter of the warm floor: this is how the temperature in the circuit is controlled, and if the limiter breaks, the efficiency of the boiler will decrease, and in winter the risk of condensation will increase

d4 - excessively large temperature difference. Check out bypass valve and pump, deal with the pressure in the boiler. The return temperature can be much lower than the supply temperature, which is why problems arise in the operation of the device. The boiler gives an error so that condensation does not form later, there are no breakages or malfunctions.

d5 - defect of the external temperature sensor. Check the meter as well as the connection wire.

d7 - error in the control valve. Determine what is wrong with the regulator. Make sure the connection cable is in order.

In the Bosch Gaz 6000 W WBN 6000-24C RN, a failure with the d7 code indicates a defective gas valve. Look into it and replace if necessary through the gas men. The case may also be in the connecting wire.

Category # 4 - device problems on E

E0 - There is a problem inside the circuit board. Inspect electrical contacts; replace unusable circuit board.

E2 - the temperature sensor does not work in the flow line. The error is also defined as a problem in the NTC feed line. Ring the temperature sensor for an open, short circuit, or other malfunction. Inspect its cable. Clean the oxidized wires and connect them in case of a broken circuit.

The printed circuit board may break after a thunderstorm, and in this case, separate microchips and a double diode in the harness are replaced, in the image there is a board from the Bosch boiler

E9 - the temperature limiter has tripped.

Complete the following steps:

1. Check the connections to the circuit board for oxidation and mechanical damage. Clean and connect the cores, if necessary.
2. Inspect the heat exchanger temperature limiter. Make sure its wire is intact. Replace items if repair is not possible.
3. Do the same with the flue gas temperature limiter. The problem may be tearing or melting.
4. See if the pressure in the system has dropped. Pour water until it normalizes.
5. Evaluate pump performance by starting. It could just jam. If the malfunction is serious, replace pump.
6. Inspect the fuses on the circuit board and power supply cover.
7. The boiler could draw in too much air. Remove it.
8. Inspect the water circuit of the heat exchanger. Descale and restore throughput flush the heat exchanger.

EA - when on, no flame was detected.

EA is one of the most common mistakes that many factors cause, but cleaning it up with ignition and control electrodes, such as fine-grained sandpaper, may be enough to eliminate it.

You will have to work out many options that cause this error:

1. Take a look at the position of the gas tap. Open it all the way.
2. Determine the fuel pressure if the error remains. If the standard parameters do not meet, contact the boiler master or the gas service.
3. Check mains voltage. With an indicator below the norm will help Voltage regulator or autotransformer.
4. Inspect the mechanical contacts of the wires. Strip them and put them together.
5. Release the chimney from clogging and contamination. Find out the concentration of carbon dioxide. Check serviceability.
6. Clean the ignition electrode from soot. Straighten it if it is bent, and install as required in the instructions.
7. Call the gas control sensor with a multimeter for an open or short circuit. Repair or replace.
8. Descale the heat exchanger.
9. Check the condition of the gas valve. A full inspection, repair and replacement must be carried out by the gasman.
10. Inspect the circuit board and replace if there are no other options.

In Bosch Eurostar products, the EA designation indicates the absence of an ionization current. Inspect the ionization electrode and take other steps among the above.

Er - the boiler does not work correctly. Check all units of the device and repair them in the event of a malfunction.

Category # 5 - boiler errors on F

F0 - in gas boilers Bosch means a malfunction inside the device. Check the condition and tightness of the connection of the plug contacts and wires to the electronic board. If the connections are broken or oxidized, repair the board. If not, it should be replaced.

If you took out the board and identified the problem in it, then take it to the service center - there they will restore the tracks and solder the parts

F7 - when the boiler is off, a flame is detected.

Take the following steps:

1. Clean or replace electrodes.
2. Check connecting wire.
3. Ensure that the exhaust ducts are in good condition. Remove dirt. Repair the system if necessary.
4. Check the humidity of the board. Dry it.

In boilers of the Bosch Eurostar ZWE and Bosch Eurostar ZSE ranges, the indicated error warns of an incorrect ionization signal. There may be tears or cracks between the cable and the ionization electrode - check this. Look for moisture in the Heatronic junction box.

FA - after turning off the gas supply, a flame was detected. Inspect and, if necessary, replace the gas valve, its wiring. But not on their own. Check electrodes and connecting cables. Inspect the exhaust gas channel as well, clean, repair if necessary.

In Bosch Eurostar boilers, the FA code indicates that when the regulator is turned off, the ionization current is maintained. It is worth looking at gas fittings and their wiring, an ionization electrode.

Fd - too long pressing the button. An error pops up after half a minute of continuous holding the button. Press it again and do not hold for longer than 30 seconds.

Other Bosch Gas Boilers Errors

These are not core codes, and they do not fall into the main categories. Occur in all or only specific models.

11 - corresponds to the above error E9. Occurs on a Bosch BWC 42 boiler.

Professional washing of the heat exchanger: the prevention of E9 error includes flushing once every 2 years to maintain the boiler efficiency, and for this you will need a 20-liter tank and washing solution

50 - there is no flame. Appears on Bosch Gaz 4000 W ZWA 24-2 A and 24-2 K boilers.

Follow these steps:

1. Inspect the protective cable and restore its integrity.
2. Open the gas tap to maximum.
3. Determine the gas pressure in the line. If there is a discrepancy with the nominal indicator for the passport of the device, call the gas service.
4. Check if there is voltage, if it meets the normal value.
5. Look into the chimney and clean it if necessary.
6. Test gas adjustment to minimum and maximum levels. Adjust according to the tables of instructions.
7. Check gas control relay and replace if necessary.
8. Inspect gas fittings for external damage. Do not check its performance, do not repair or replace. Let the gasman or gas boiler master do it.
9. Clean and rinse the heat exchanger.

70 - breakdown of the differential relay at startup. The most common cause of this error may be problems in the relay itself. Inspect his condition, determine the resistance. Change to a new one if the resistance does not match the nominal.

There may also be mechanical damage to the wires and contacts going to the relay. If so, then you need to restore the connection. Another cause may be improper fan configuration or failure. Reconfigure the device. It did not help - repair or buy a new one.

b1 - no coding plug detected. Insert it correctly. If the error persists, ring the plug and replace if broken.

P - it is not possible to determine the type of boiler. Set its type.

A coaxial chimney can have a complex pattern due to an electric supercharger, but according to general requirements for quality work, its total length should not exceed 4 meters

se - The heating system is not full enough. Add water and check the result. An error also appears due to depressurization of heating pipes and leaks. Lower the heating temperature and find the problem spot. Seal joints and seal leaking points.

With hot pipes this will not work - a small amount of water will evaporate quickly. If the heating pipes are in order, remove and wash the heat exchanger.

There is also code 23. This is not a mistake, but an indicator of the type of gas used.

Conclusions and useful video on the topic

Resolving similar errors C4 and C6 and installing a filter to collect condensate:

A short video tutorial on how to troubleshoot an EA error:

What to do when the pressure drops in the heating system, setting the expansion tank:

Definition of a problem with the fan and its solution:

We examined the errors of various Bosch boilers sorted by the first letter, as well as other codes that sometimes pop up on displays. Before fixing the problem with the code, try reconnecting the device, look at the position of the taps and control knobs. It did not help - disassemble the device and proceed step by step as required by the prescription.

The old Bosch gas boiler may need professional repairs, despite the reliability of this technique as a whole. Only certified craftsmen and gas workers are allowed to touch the gas pipes.

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