Condensing Gas Boilers FAQ

An A5 error code indicates that the boiler's water pressure is running low.

• The most likely time that you may see this error code is just after the boiler has been installed and run, and it's typically an indication that the water fill procedure wasn't correctly followed.
  To rectify this, please refer to the "System Filling" section of your installation manual.

• If the issue remains ongoing even after ensuring that the boiler's water pressure is correct, it could be the case that water is being lost in the overall heating system somewhere. We recommend that a contractor examine the boiler and the home's heating system for evidence of water leakage.

If you no longer have the printed copy of the manual, you can download an electronic version from this page.

You will notice two icons to the left of the boiler's display screen. One is a Radiator and the other is a Faucet:

• Radiator Icon: This icon is always illuminated when the boiler is powered on. If you need to adjust the space heating temperature, press the MODE button and the display screen will change to show the current set point. The + and - buttons can then be used to adjust the temperature setting. Once you have made the adjustment, simply wait for 5 seconds and the control will revert back to normal operation and the Radiator icon will remain illuminated.
• Faucet Icon: The only time that this icon illuminates is when the user manually goes into the settings to change the temperature of the domestic hot water. If you want to adjust the temperature of the domestic hot water, press the MODE button until the Faucet icon illuminates. The + and - buttons can then be used to adjust the temperature setting. Once you have made the adjustment, simply wait for 5 seconds and the control will revert back to normal operation with the Faucet icon turning off and the Radiator icon turning back on.

Early production runs of the Singular boiler inadvertently included those wires, and they will be removed from current and future production of the product.

In short:

• The two blue "Air Handler" wires have NO purpose at all.
• Please do NOT attempt to connect them to anything or cut them off. Simply tuck them neatly out of the way.
• The Singular boiler CANNOT be connected to an air handler.

At the bottom of the boiler you will see two brown wires labelled "Zone Control Wire". Please connect your thermostat, or zone control's end switch, to these wires.

For further details and wiring diagrams, please download the latest manuals from this page.

This is a perception that is most commonly noted by owners that have recently switched to a combi-boiler or a tankless water heater after moving away from using a heated storage tank to produce and store Domestic Hot Water (DHW).

Here's why:

Heated Storage Tanks - The water contained in such a water heater is being heated throughout the day and night, regardless of whether you are using it or not.

The benefit of course, is that the stored water is already hot and ready for use at any time.

However, that means that energy is being used just to keep a large supply of hot water on standby. You are paying to heat and store water all the time, just to use it sporadically through the day.

In addition to the ongoing energy use, you will also only be able to use as much hot water as the tank can store, and once the hot water is depleted, you will need to wait until the fresh cold water has been heated up and ready to use.

Combi-Boilers & Tankless Water Heaters - These types of water heating products only produce hot water when the owner opens a hot fixture somewhere in the home.

This means that no hot water is stored in the product, and so when you open a fixture in the home the water heater will ignite and then start heating the cold water that is flowing through its heat exchanger now. That does mean that there is a small delay in the delivery of hot water to the fixture, and if you previously used a heated storage tank you may notice it.

The benefits though, are significant:

• You are only paying for energy while the product is activated and producing hot water on-demand. When you close the hot water fixture, the product is going to shut down and go back into standby mode.
• You are not limited to a fixed amount of hot water that will deplete and then run cold. As long as you have a hot water fixture open and the product has activated, you will have endless hot water from that fixture until you close it.

Plumbing Distance:

Regardless of whether you are using a heated storage tank, a combi-boiler, or a tankless water heater to produce your home's hot water, there is another delay that must be recognized.

There will still be a delay in the delivery of hot water as the plumbing between the product and the fixtures will contain cold water that will need to be pushed ahead of the hot water that's heading towards the open fixture.

Simply put: The longer the run of plumbing, the longer it will take for the hot water to arrive where it's needed.

Potential Solutions

For the majority of users, the small delay in hot water being produced and then reaching their hot fixtures is of no concern. It is a normal dynamic of hot water that is produced by a combi-boiler or a tankless water heater, and the owner is instead focused on enjoying the lower energy costs!

• If you have a fixture that is particularly far away from the water heating product, and it's one that you frequently use and the delay is problematic for you, then you could use an electric mini-tank water heater as booster. These water heaters are typically 120v and should be installed close to the distant hot fixture and in-line between the main water heating product and the distant fixture. For further details regarding our family of Tronic 3000T electric mini-tank water heaters, please visit this page.

• If you would prefer to reduce the wait time for hot water at all hot fixtures in the home, then we recommend consulting a licensed plumber to discuss the options for installing a recirculating hot water plumbing arrangement. Please visit this page to search for a contractor in your area. Typically one loop of hot water plumbing will leave the water heating product, travel around the home, and then back to the product. Short plumbing lines to each hot water fixture will then branch off the main loop. A pump and a timer will be used to circulate the water around that loop occasionally, which will also activate the combi-boiler or tankless water heater, and leave hot water in the plumbing loop around the home. The next time you open a hot water fixture, you will have less of a wait time for cold water to flush through, as it is pre-heated from the last time that the recirculation pump ran.
  Important! Before deciding to install a recirculation loop, be certain that your combi-boiler or tankless water heater can safely be installed in such an application. Some models are designed to be supplied with cold water only and may be damaged if supplied with heated water that is returning from a circulation loop. Consult the literature that came supplied with your product. If you no longer have the printed literature that came supplied with your product, an electronic copy can be downloaded from our manuals download page.

Warning! Water temperature that is over 120of (50oC) can cause immediate scalding, burns, or even death. As with all products that produce domestic hot water, we recommend setting the temperature as low as possible while still satisfying your needs at the hot water fixtures in your home.

To Adjust The DHW Output Temperature:

• Press The "Mode" button the front of the display control until the "Faucet" icon is illuminated.
• Use the "+" or "-" buttons to select your desired DHW temperature (please see the Warning note at the top of this section!).
• The control will return back to normal operation after several seconds if you do not push any buttons.

For further details regarding all of the above maintenance topics, please refer to the User Manual and Installation Manual that came supplied with your boiler.

If you no longer have the hard copies, we have made electronic copies available to you for download via this webpage.

Yes, selecting the "H7" mode will allow you to see the temperature of the DHW as it leaves the boiler and heads to your home's fixtures.

To Access "H7" Mode:

• Press the "Mode" button repeatedly until "H7" is displayed on the screen.
• The display will alternate between showing "H7" and the actual temperature of the DHW from the boiler.
• The control will return back to normal operation after several seconds if you do not push any buttons.

For further details regarding all of the above maintenance topics, please refer to the User Manual and Installation Manual that came supplied with your boiler.

If you no longer have the hard copies, we have made electronic copies available to you for download via this webpage.

Unless you have used the "Mode" button to temporarily move into a different mode, the reading that is shown on the boiler's display at all times during normal operation is the temperature of the water that is being supplied out to the home's heating system.

If you would like to see the temperature of the water that is returning back to the boiler from the heating system, you will need to go into "H9" mode.

To Access "H9" Mode:

• Press the "Mode" button until "H9" is displayed on the screen.
• The display will alternate between showing "H9" and the temperature of the heating water returning to the boiler.
• The control will return back to normal operation after several seconds if you do not push any buttons.

For further details regarding all of the above maintenance topics, please refer to the User Manual and Installation Manual that came supplied with your boiler.

If you no longer have the hard copies, we have made electronic copies available to you for download via this webpage.

Warning! The gas conversion process must ONLY be carried out by a service person who is qualified to work on gas combustion equipment, and possesses a properly calibrated gas combustion analyzer. If you are in need of a qualified service person in your area, please use this contractor search page.

No, we do not produce variants of the Singular that are specific to gas types. All Singular boilers come setup and ready for installation into NG applications, but we also include a free of charge LP gas conversion kit in the boiler's packaging too.

The correct installation of the conversion kit, and subsequent setup of the boiler, will require a gas-qualified service person with a calibrated combustion analyzer, a #2 Phillips screwdriver, and a 5/32" (or 4mm) Allen wrench.

Illustrated step by step instructions of the gas conversion procedure are provided in the Installation manual that came supplied with your boiler. If you no longer have the hard copy, we have made electronic copies available to you for download via this webpage.

Warning! The DIP switches are used to control certain functions and limits of the boiler, and must ONLY be adjusted by a service person who is qualified to work on gas combustion equipment. If you are in need of a qualified service person in your area, please use this contractor search page.

For specific details regarding all of the DIP Switch settings and procedures mentioned below, please refer to the Installation Manual that came supplied with your boiler. If you no longer have the manual, we have made electronic copies available to you for download via this webpage.

The DIP switch block is mounted on the boiler's main circuit board, and is numbered 1 through 8 (top to bottom):

• Switch #1 (labeled "FTC"): Enables/Disables the exhaust temperature limit (Enabled = switch in the On position / Disabled = switch in the Off position). This switch comes from the factory set to Off and limits the exhaust temperature to a maximum of 149° F (65° C), allowing for the use Schedule 40 PVC exhaust venting. In applications where the exhaust temperature will be higher than 149° F (65° C) the switch must be set to On and vent materials approved for those higher temperatures MUST be used. For full details, please refer to the Installation Manual.
• Switch #2 (labeled "PROGRAM"): This is the data change mode switch, and comes from the factory set to Off. When the installer is ready to program the boiler's control to set the Outdoor Reset heating curve and also the elevation that the boiler is installed at, this switch must be set to On to put it into the programming mode and then switched back Off to lock in the changes.
• Switches #3 and #4 (labeled "EX 1" and "EX 2"): The position of these two switches is dependent on the diameter and length of the exhaust flue installation, and MUST be set by the installer while referring to the table that is included in the Installation Manual.
• Switch #5 (labeled "N/A"): Not used. No adjustment needed.
• Switch #6 (labeled "MIN"): Minimum heat capacity switch. MUST be used by the installer when using a combustion analyzer to finalize the setup of the boiler.
• Switch #7 (labeled "MAX"): Maximum heat capacity switch. MUST be used by the installer when using a combustion analyzer to finalize the setup of the boiler.
• Switch #8 (not labeled): Not used. No adjustment needed.

This is a perception that is most commonly noted by owners that have recently switched to a combi-boiler or a tankless water heater after moving away from using a heated storage tank to produce and store Domestic Hot Water (DHW).

Here's why:

Heated Storage Tanks - The water contained in such a water heater is being heated throughout the day and night, regardless of whether you are using it or not.

The benefit of course, is that the stored water is already hot and ready for use at any time.

However, that means that energy is being used just to keep a large supply of hot water on standby. You are paying to heat and store water all the time, just to use it sporadically through the day.

In addition to the ongoing energy use, you will also only be able to use as much hot water as the tank can store, and once the hot water is depleted, you will need to wait until the fresh cold water has been heated up and ready to use.

Combi-Boilers & Tankless Water Heaters - These types of water heating products only produce hot water when the owner opens a hot fixture somewhere in the home.

This means that no hot water is stored in the product, and so when you open a fixture in the home the water heater will ignite and then start heating the cold water that is flowing through its heat exchanger now. That does mean that there is a small delay in the delivery of hot water to the fixture, and if you previously used a heated storage tank you may notice it.

The benefits though, are significant:

• You are only paying for energy while the product is activated and producing hot water on-demand. When you close the hot water fixture, the product is going to shut down and go back into standby mode.
• You are not limited to a fixed amount of hot water that will deplete and then run cold. As long as you have a hot water fixture open and the product has activated, you will have endless hot water from that fixture until you close it.

Plumbing Distance:

Regardless of whether you are using a heated storage tank, a combi-boiler, or a tankless water heater to produce your home's hot water, there is another delay that must be recognized.

There will still be a delay in the delivery of hot water as the plumbing between the product and the fixtures will contain cold water that will need to be pushed ahead of the hot water that's heading towards the open fixture.

Simply put: The longer the run of plumbing, the longer it will take for the hot water to arrive where it's needed.

Potential Solutions

For the majority of users, the small delay in hot water being produced and then reaching their hot fixtures is of no concern. It is a normal dynamic of hot water that is produced by a combi-boiler or a tankless water heater, and the owner is instead focused on enjoying the lower energy costs!

• If you have a fixture that is particularly far away from the water heating product, and it's one that you frequently use and the delay is problematic for you, then you could use an electric mini-tank water heater as booster. These water heaters are typically 120v and should be installed close to the distant hot fixture and in-line between the main water heating product and the distant fixture. For further details regarding our family of Tronic 3000T electric mini-tank water heaters, please visit this page.

• If you would prefer to reduce the wait time for hot water at all hot fixtures in the home, then we recommend consulting a licensed plumber to discuss the options for installing a recirculating hot water plumbing arrangement. Please visit this page to search for a contractor in your area. Typically, one loop of hot water plumbing will leave the water heating product, travel around the home, and then back to the product. Short plumbing lines to each hot water fixture will then branch off the main loop. A pump and a timer will be used to circulate the water around that loop occasionally, which will also activate the combi-boiler or tankless water heater, and leave hot water in the plumbing loop around the home. The next time you open a hot water fixture, you will have less of a wait time for cold water to flush through, as it is pre-heated from the last time that the recirculation pump ran.
  Important! Before deciding to install a recirculation loop, be certain that your combi-boiler or tankless water heater can safely be installed in such an application. Some models are designed to be supplied with cold water only and may be damaged if supplied with heated water that is returning from a circulation loop. Consult the literature that came supplied with your product. If you no longer have the printed literature that came supplied with your product, an electronic copy can be downloaded from our manuals download page.

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 bulletinwill 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.