Errors in Bosch gas boilers: deciphering common errors and eliminating them

Are you familiar with the situation when you see an error code and don’t even know roughly what it means? Perhaps you always lose the instructions for your household appliances, and searching for information on the Internet turns up nothing. In this article, we indicated the errors of Bosch gas boilers, their explanations and the necessary steps to eliminate them. It won’t hurt you to remember it if you also have a Bosch boiler and an error suddenly appears on its display. It will be good if the article helps you at the most needed moment.

There is usually not enough space on boiler displays, so the problem has to be transmitted using a short code. Thanks to our material, you will be able to navigate all the main types of errors. You won't be afraid of simple letters and numbers that appear on the boiler.

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

Bosch boiler error categories

The Bosch company produces boilers of different capacities for heating running water, home heating and underfloor heating systems. Series devices Eurostar manufactured under a common brand Junkers Bosch.

Bosch and Bosch Eurostar boilers 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.The failures themselves do not indicate a problem with the equipment.

Bosch Gaz 6000 W WBN 6000-24C RN boiler control panel: this device was adapted to Russian conditions and is the first domestic boiler under an 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.

If there is an error, you need to find out the reason from its decoding, inspect a separate part of the device and, based on its condition, determine that the notification did not appear by chance. In the worst case, owners face repairs, replacement of parts or the entire device. It should be remembered that ordinary consumers should not touch the parts through which gas enters the boiler. Most errors appear not after breakdowns, but due to operating conditions.

Problems in boiler operation are not always listed as errors. Difficulties also arise with the temperature of the supplied water. The liquid sometimes becomes too cold or hot. Only a gas boiler specialist 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 inconveniences appear, such as long heating times and noise of the water flow. Constant problems with starting the boiler indicate low gas pressure, clogged discharge paths or a breakdown in the electrical circuit.

Circulation pump for a Bosch gas boiler: this part of the device accelerates the heated liquid through the heating system, due to which the coolant cools more slowly, the second heating cycle becomes shorter, and subsequent ones approximately correspond to the second

These are just general problems. Errors by 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 appear 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 — there is an emission of flue (exhaust, flue) gases in the combustion chamber. All you need to do is see if dirt has accumulated on the heat exchanger and remove it. Usually this is enough.

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

A4 — release of exhaust gases at the flow fuse. Inspect the flue gas exhaust line.

A6 — the combustion chamber temperature sensor was not detected. In this case, check the contact wire and combustion chamber temperature sensor for damage.

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

A8 — there is no connection to the e-BUS bus. You need to inspect the control knobs and connecting cable.

A9 — incorrect installation of the hot water temperature sensor.Check the installation location. If necessary, remove the sensor, reinstall it and add thermal paste.

The hot water temperature sensor is installed using a 15 wrench, in the photo there is a device for Bosch and Junkers

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

On Bosch Eurostar devices, the AC error indicates a problem with the interaction between the connected module and the Heatronic. You should check the wire between them.

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

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

Category #2 - breakdowns on C

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

C3 — corresponds to the above-described 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 not working. We need to see what happened to the relay.

There are two ways out of this situation:

1. Remove the relay and blow out the tubes that come from it.
2. Use a multimeter to determine if there is a short circuit, open circuit, or non-compliance with the resistance rating. Replace the 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 using a hair dryer. Do an open and short test. Remove excess from the chimney. It could be frost, ice, etc.

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

CC — external temperature sensor not found. In Bosch Eurostar series boilers, the CC code indicates a break in this temperature sensor. Look for damage and possible breakage of the meter and contact cable.

C.E. — the pressure in the heating system is too low. If the pressure gauge indicates the red zone, add water through the water supply tap. If the pressure gauge needle is in the green area, then there is a problem with it. Sometimes the problem occurs in the membrane or microswitch.

Category #3 - faults on d

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

d3 — there is no jumper 161 on ST8. Find out if there is a jumper. If yes, also inspect the external stopper and insert the plug correctly.

Scheme of operation of the underfloor heating regulator-limiter: 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 bypass valve and pump, figure out the pressure in the boiler. The return flow temperature can be much lower than the supply temperature, causing problems with the unit's operation. The boiler gives an error so that condensation does not form later, there are no breakdowns 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 model, a failure with code d7 indicates a faulty gas fitting. Look into it and replace it if necessary through the gas workers. It could also be a problem with the connecting wire.

Category #4 - device problems on E

E0 - a problem inside the printed circuit board. Inspect the electrical contacts, replace the unusable board.

E2 — the temperature sensor in the supply line does not work. The error is also identified as a problem in the NTC supply line. Check the temperature sensor for open circuit, short circuit and other faults. Inspect its cable. Clean oxidized wires and connect them if the circuit breaks.

The printed circuit board may break after a thunderstorm, in which case the individual microcircuits and the dual diode in the harness are replaced, the picture shows a board from a Bosch boiler

E9 — the temperature limiter has tripped.

Follow these steps:

1. Check connections to the board for oxidation and mechanical damage. Clean and connect the wires 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 for the flue gas temperature limiter. The problem may be rupture or melting.
4. See if the pressure in the system has dropped. Add water until it returns to normal.
5. Assess the performance of the pump by starting. It could just get jammed. If the malfunction is serious, replace the pump.
6. Inspect the fuses on the board and power supply cover.
7. The boiler may have taken in too much air. Remove it.
8. Inspect the water circuit of the heat exchanger. Remove scale and restore throughput, flush the heat exchanger.

E.A. — no flame detected when switched on.

EA is one of the most common errors that is caused by many factors, but to eliminate it, cleaning the ignition and control electrodes, for example with fine-grained sandpaper, may be enough

There are many possibilities to work through that cause this error:

1. Take a look at the position of the gas supply valve. Open it all the way.
2. Determine the fuel pressure if the error remains. If the standard parameters do not comply, contact a boiler technician or gas service.
3. Check the power supply voltage. If the reading is below normal, it will help Voltage regulator or autotransformer.
4. Inspect the mechanical contacts of the wires. Strip them and connect them.
5. Free the chimney from blockages and dirt. Find out the concentration of carbon dioxide. Check the functionality.
6. Clean the ignition electrode from soot. Straighten it if it is bent and install it according to the instructions in the instructions.
7. Check the gas control sensor for an open or short circuit with a multimeter. Repair or replace.
8. Remove scale from the heat exchanger.
9. Check the condition of the gas fittings. A full inspection, repair and replacement should be carried out by a gas technician.
10. Inspect the electronic board and replace if there are no other options.

In devices of the Bosch Eurostar line, the designation EA indicates the absence of ionization current. Inspect the ionization electrode and follow other steps listed above.

ER — the boiler is not working correctly. Check all units of the device and repair them if there is a malfunction.

Category #5 - boiler errors on F

F0 - in Bosch gas boilers it 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 torn or oxidized, repair the board. If not, it should be replaced.

If you have taken out the board and identified a problem with it, then take it to a service center - they will restore the tracks and solder the parts

F7 — when the boiler is turned off, a flame is detected.

Take these steps:

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

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

F.A. — after turning off the gas supply, a flame was detected. Inspect and, if necessary, replace the gas fittings and their wiring. But not on your own. Check electrodes and connecting cables. Also inspect the gas exhaust channel, clean it, repair it if necessary.

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

Fd — pressing the button too long. The error appears after half a minute of continuously holding the button. Press it again and do not hold it for more than 30 seconds.

Other errors of Bosch gas boilers

These are not the main codes and they are not included in the main categories. Occurs in everyone or only in specific models.

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

Professional flushing of the heat exchanger: prevention of error E9 includes flushing once every 2 years to maintain boiler efficiency, and for this you will need a 20-liter container and a flushing 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 valve to maximum.
3. Determine the gas pressure in the line. If there is a discrepancy with the nominal value according to the device passport, call the gas service.
4. Check if the voltage is normal.
5. Look down the chimney and clean it if necessary.
6. Test the throttle adjustment to minimum and maximum levels. Adjust based on the instruction tables.
7. Check the gas control relay and replace if necessary.
8. Inspect the gas fittings for external damage. Do not check its functionality, do not repair or replace it. Let a gas engineer or a gas boiler technician do this.
9. Clean and flush the heat exchanger.

70 — breakdown of the differential relay during startup. The most common cause of this error may be problems in the relay itself.Inspect its condition, determine the resistance. Replace with a new one if the resistance does not match the nominal value.

There may also be mechanical damage to the wires and contacts going to the relay. If this is the case, then you need to restore the connections. Another reason may be incorrect fan settings or failure. Reconfigure the device. If it doesn’t help, repair it or buy a new one.

b1 — coding plug not detected. Insert it correctly. If the error does not disappear, ring the plug and replace it if damaged.

P — it is impossible to determine the type of boiler. Set its type.

A coaxial chimney may have a complex pattern due to an electric blower, but according to the general requirements for high-quality operation, its total length should not exceed 4 meters

se — the heating system is not filled enough. Add water and check the result. The error also appears due to depressurization of heating pipes and leaks. Reduce the heating temperature and find the problem area. Seal joints and seal leakage points.

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

There is also code 23. This is not an error, but an indication of the type of gas used.

Conclusions and useful video on the topic

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

Brief video instructions on how to resolve the EA error:

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

Identifying the fan problem and solving it:

We looked at the errors of different Bosch boilers sorted by the first letter, as well as other codes that sometimes appear on the displays.Before correcting the problem using the code, try reconnecting the device, look at the position of the taps and control knobs. If it doesn’t help, disassemble the device and proceed step by step as required by the instructions.

An old Bosch gas boiler may need professional repairs, despite the reliability of this equipment in general. Only certified craftsmen and gas fitters have the right to touch gas pipes.

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