Bosch Thermotechnology

Condensing Gas Boilers FAQ

Safety Notice - This is a gas-fired product, and only professionals who are qualified to work on live gas equipment should do so.

An "EA" code displayed is an indication that the boiler attempted to ignite, but either failed to achieve combustion or the combustion was not seen by the flame sensor.

There are many potential causes of such an issue, but the most common are listed below.

1. Using a manometer, check that the static gas pressure at the boiler is within the required range;

NG: 3.5" to 10.5"

LP: 8" to 13"

If the static gas supply pressure to the boiler is outside of those parameters, please assess the gas supply to the property and the gas installation to the boiler to identify the problem and resolve.

2. When the boiler tries to fire, are you seeing a slight gas pressure drop on your manometer?

Yes: This indicates that the gas valve is at least opening, so please check the following;

• Ensure that the ignition electrodes are sparking.

• Check for loose or disconnect wires, and resolve if found.

• Check that the air supply to the boiler is adequate and free of blockage.

• Check that the condensate trap is not backed up.

• There is a diaphragm valve located within the top of the plastic air tube that runs into the bottom of the inducer fan, check to make sure that the diaphragm is not stuck.

No: Please contact our technical support team at 1-800 283 3787 Monday to Friday. The very best way to assist you would be for you to be at the boiler with your manometer, a multimeter, and a combustion analyzer.

Safety Notice - This is a gas-fired product, and only professionals who are qualified to work on live gas equipment should do so.

The Greenstar family of boilers all come from the factory setup to run in NG gas applications.

If you are installing a new Greenstar boiler into an LP gas application, or if an existing Greenstar boiler is in a home that is having its gas supply changed from NG to LP, the boiler must be reconfigured for use with LP fuel.

1. The process requires the installation of the LP code plug that came supplied with the boiler, and then recommissioning of the boiler by using a flue gas combustion analyzer and making careful adjustments to the gas throttle.

2. A basic overview of the process can be found on this service bulletin, here .

3. For full details however, we recommend that you refer to the boiler's installation manual. If you have misplaced the manual, you can find it on this page available for download.

Safety Notice - This is a gas-fired product, and only professionals who are qualified to work on live gas equipment should do so.

An "E9" error code will be displayed under one of two conditions:

1. The heat exchanger safety high limit switch has tripped. Please check the following potential causes;

a. Check the heat exchanger high limit switch and wiring harness for continuity or shorts, and replace if defective.

b. Check the heat exchanger to see if it is clogged internally.

c. Check the boiler water pressure to ensure that it is within 14.5psi (1 bar) when system is cold and a maximum of 21.75psi (1.5 bar) when heating.

d. Check for correct operation of the internal circulator pump. Details can be found on this service bulletin .

e. Check the bolts that hold down the heat exchanger inspection cover for correct torque. Further details are found on this service bulletin .

f. Perform a combustion test with your flue gas analyzer to ensure that the gas/air ratio is within the required specifications. Full details on the CO2 and O2 requirements, and how to measure and adjust them, can be found in the product's installation manual. If you have misplaced the manual, you can find it on this page available for download.

2. The flue gas temperature limiter has tripped. Please check for the following potential causes;

a. Check the flue gas limiter and wiring harness for continuity or shorts, and replace if defective.

b. Ensure that all connections in both the internal flue collection parts and the external flue venting installation are correctly sealed and not leaking combustion waste gases or blocked in any way.

Backflow prevention devices in the water supply (including devices installed within a water meter) can result in a build-up of water pressure that could potentially damage the boiler or other appliances in the property.

Further details can be found in this service bulletin .

As part of a complete startup commissioning of a newly installed Greenstar boiler, we recommend that the installer ensures that the circulator pump can be spun freely before filling the boiler with water.

Further details can be found on this service bulletin .

Yes.

As with all heating appliances it is important to perform all required maintenance on time and correctly.

This will ensure that the boiler continues to operate safely, efficiently, and will reduce the risk of premature failure of any component within the product.

For full details of the required maintenance actions, we recommend that you refer to the boiler's installation manual. If you have misplaced the manual, you can find it on this page available for download.

Safety Notice - This is a gas-fired product, and only professionals who are qualified to work on live gas and 120v electrical equipment should do so. If you are in need of a qualified professional in your area, please use this contractor search page .

If you are certain that the leak is definitely coming from the heat exchanger itself, and not a pipe or any other component that's connected to it, then it must be replaced immediately.

To determine the correct heat exchanger part# for your particular size of GB142 boiler, please download this parts diagram .
You can then order a new heat exchanger through your distributor of choice.
For instructions on how to replace the heat exchanger, please refer to this service bulletin .

We also recommend testing the chemistry of the water that is being circulated through the boiler, as one of the main causes of a heat exchanger failure is water quality that does not meet the required parameters, or the use of a chemical additive that is not approved for use with this product.
For specific details regarding water quality and approved additives, please refer to this service bulletin .

Safety Notice - This is a gas-fired product, and only professionals who are qualified to work on live gas and 120v electrical equipment should do so. If you are in need of a qualified professional in your area, please use this contractor search page .

Yes, we recommend an annual maintenance plan that includes, but is not limited to, the following points*;

1. Visually checking for corrosion or water leaks inside the boiler.

2. Checking the gas piping inside the boiler for signs of leaks, corrosion, or damage.

3. Check the gas supply piping and pressure supplied to the boiler to ensure that no leaks or damage is evident, and that the supply pressure is between 3.5"WC to 11.5"WC (for NG installations), or 8"WC to 13"WC (for LP installations).

4. Check the gas/air ratio, and adjust if needed.

5. Measure the carbon monoxide (CO) content.

6. Pressure test the heating system.

7. Inspect the air intake piping and exhaust venting to ensure that there is no damage, leaks, or blockages.

8. Measure the ionization current.

9. Inspect and clean the heat exchanger

a. Heat exchanger cleaning video

b. Heat exchanger cleaning service bulletin

*For full details of the recommended maintenance points, and instructions how to carry out the steps and tests, please refer to both the GB142 Installation Manual and the GB142 Service Manual. Both of these documents can be downloaded from this page .

Safety Notice - This is a gas-fired product, and only professionals who are qualified to work on live gas and 120v electrical equipment should do so. If you are in need of a qualified professional in your area, please use this contractor search page .

There are two fuses in the GB142; One in the UBA3, and one in the External Connection board.
If you have confirmed power to the boiler, the power switch is on but the display is blank, then it is the fuse that is located in the UBA3 that must be checked.
Please refer to Section 8 of the GB142 Service Manual for detailed instructions of how to locate and test this fuse. If blown, the fuse must be replaced with a working ceramic 5A 250V fast-blow fuse (F5AH, 250V).

If the new fuse blows too, then there may be an internal component of the boiler that has failed.

To determine which component may* be the cause of the problem, please do the following;

1. Turn the power switch to the Off position.

2. Unplug the 120V wiring connectors to the fan, the hot surface ignitor (HSI), and the boiler pump.

3. Turn the power switch back on.

a. If the fuse blows, then there may be a problem with the wiring inside the boiler. Check for damage or loose connections in the wiring harnesses.

b. If the fuse did not blow, then it could indicate that one of the components that was unplugged in Step #2 is causing the problem. Turn the power switch back off, and then proceed to Step #3.

4. Plug the 120V connector back into the fan, turn the power back on.

a. If the fuse blows, then the fan is defective and must be replaced.

b. If the fuse does not blow, move to Step 4.

5. Turn the power switch back Off.

6. Plug the connector back into the HSI, turn the power back on.

a. If the fuse blows, then the HSI must be replaced.

b. If the fuse does not blow, move to Step 6.

7. Turn the power switch back Off.

8. Plug the connector back into the boiler pump, turn the power back on.

9. If the fuse blows, the boiler pump must be replaced.

*This is a guide only, and Bosch is not responsible for any parts purchased that may not ultimately be the cause of an issue. We advise that contractors keep a stock of key service parts which can then be used to help diagnose potential issues.

Safety Notice - This is a gas-fired product, and only professionals who are qualified to work on live gas and 120v electrical equipment should do so.
If you are in need of a qualified professional in your area, please use this contractor search page .

A "3L" code typically suggests that there may be an issue with the fan, the UBA3, or any connections between them.
After turning the power switch Off, the first thing to check is to make sure that all wiring connections between the fan and the UBA3 are plugged in securely and that there is no obvious damage to the connectors or the wiring.
After that, it's recommended to try replacing* the fan to see if the issue is resolved, and then the UBA3.

For further details, please refer to the 3L troubleshooting steps that are explained in the GB142 Service Manual, which can be downloaded here .

*This is a guide only, and Bosch is not responsible for any parts purchased that may not ultimately be the cause of an issue. We advise that contractors keep a stock of key service parts which can then be used to help diagnose potential issues.

Safety Notice - This is a gas-fired product, and only professionals who are qualified to work on live gas and 120v electrical equipment should do so. If you are in need of a qualified professional in your area, please use this contractor search page .

A "6A" error code indicates that the boiler is not sensing ionization after making four attempts to ignite the burners.

This could mean;

1. The burners are not igniting at all. This could be caused by any of the following;

a. Incorrect orifice for the gas type.

b. Incorrect gas pressure supplied to the boiler.

c. Air/fuel ratio out of adjustment.

d. Problem with the air intake or exhaust venting.

e. Hot Surface Ignitor issue.

f. Loose wiring.

g. Power issue.

h. Failed component (for example; gas valve, HSI, UBA3 etc).

2. The burners do ignite, but the flame is not being "seen" by the control. This could be due to;

a. Dirty, or defective, ionization sensor.

b. Loose, or damaged, wiring.

c. A problem with the UBA3.

For full details of the troubleshooting steps for a "6A" code, please refer to the GB142 Service Manual, please can be downloaded here

This service bulletin will assist you further.

In addition, it is required that you retain the large aluminum nut and clip from the existing heat exchanger and transfer them to the new heat exchanger.