Buderus GB142 ingesting exhaust and locking itself out of

highoctane

Hello, I have a 14 year old Buderus GB142-30 that is giving a 6A error approx every 2 days. I have replaced the ignitor and ionization rod. Burner was cleaned in the last month with mineral oil and I replaced the top gasket on burner. At this time I also replaced the condensate trap as mine was cracked. The unit has had regular yearly maintenance but I have to replace ignitor and rod at least once a year for the past 5 years or more.

A technician was brought in and they tested for CO2 - showed 35ppm within the boiler casing. They have assessed that unit is ingesting its exhaust, causing the flame rod and ignitor to get wet from exhaust moisture, causing unit to lock out. Unit always fires up upon hitting reset button. I am told that this is because the rod and ignitor have time to dry, which makes sense.

The two solutions offered by the plumbing company are

1) doing a soap test, and

2) full boiler replacement, of course.

I should note that my exhaust and intake pipes are separated by a wall and have 15 feet of separation.

I plan to look into doing a soap test, was wondering if anyone has done this with the GB142 or if they have any advice moving forward. I am aware that this is an older boiler with a reputation for being temperamental, its just hard to stomach doing a full replacement after dropping so much money into this unit. This company also has a reputation for recommending "full replacements" on older units as opposed to taking the time to fix the problem.

Big Ed_4

Run the unit , then search around the boiler with a mirror . It will fog up.

You can also smell a leak.

highoctane

Thanks thats a great tip

EdTheHeaterMan

CO carbon monoxide is measured in PPM.

CO2 carbon dioxide is measured in percentage.

the error code 6A indicated that the boiler control is not sensing a flame when there should have a flame. You indicated that a professional tested the equipment and indicated that there may be exhaust gasses recirculating into the air intake that is causing the problem. If that is the case then one or more of these gaskets may be the problem. The maintenance technician should have these gaskets available in the event that one of them may no longer be re-useable.

Buderus 7098834 Seal, and Buderus 7098916 Seal, and Buderus 7098916 Seal, and Buderus 7098850 Seal, and Buderus 7099021 Seal, and 7098778 Sealing O ring, and Buderus 7100742 Trap seal, and Oval exhaust Seal 7098858.

Finding the leaking gasket and fixing the problem should be part of the maintenance. That is what maintenance is all about. Taking things apart cleaning and adjusting the parts, and putting them back together properly. If you are going to get charged to find what they didn't do correctly during the maintenance then maybe it is time to look for a new contractor.

Run that by the service manager and see what they say. Also ask them to bring all those part numbers with them on the next service/maintenance visit. If they resist, then ask them how are they supposed to the the factory authorized maintenance without gaskets? Would you take a water pump apart without having a spare gasket on hand? Why would take a combustion chamber apart without having the proper gaskets on hand?

Do your service trucks have more sales forms than actual repair parts?

109A_5

If it has ran good for the best part of 9 years and nothing has changed outside, probably something in the boiler has degraded. If you want to do some light reading about the 6A error code, here are some manuals.

https://s3.amazonaws.com/s3.supplyhouse.com/product_files/Buderus%20-%20GB142-30%20-%20Service%20Manual.pdf

https://s3.amazonaws.com/s3.supplyhouse.com/product_files/Buderus%20-%20GB142-30%20-%20Install%20Instructions.pdf

psb75

I just "got done" with an 18-yr-old Buderus GB 142. Am very familar with 6A error code. Did lots of maintenance on it. Mineral oil "burn-offs", igniter and flame-rod replacements, condensate trap replacement, venturi and various gaskets and seals, fan replacement, and lots of "scrapey-scrapey" on the heat exchanger. All-in-all it was a good boiler. It was the right boiler for that bldg. Good tech. and engineering for its time. Buderus (as a co.) is gone. So I replaced it with a nice, I-series Rinnai boiler. Good co. with a great reputation and good tech support and parts availability.

highoctane

Thanks everyone for the comments.

@EdTheHeaterMan - to say it has been a challenge with this boiler, and the maintenance over the years, would be an understatement. It started with the original install being done by inexperienced technicians (we found out they had never done this type of boiler, or in floor heating, after the fact.) And I agree with you, its time to find a new maintenance company. Unfortunately, with this issue looming, and I was leaving town on a trip, in the middle of a cold snap, I felt I needed to reach out to the only company that still had any track record with Buderus.

@109A_5 and psb75 -

It has run decently well for 14 years, but in the last 5-7 years, I have had issues with excessive replacement of ignitors and ionization rods. I suspect the issue I am dealing with now has been present and steadily getting worse over the years - and no one has properly identified it. When I am back at home in a week I will be able to do a proper assessment and decide on a path forward. I would like to get another 5 years out of it, we will see.

hpap

Sounds like the intake/exhaust connection on top is cracked and leaking.

That was part of recall years back I think along with gas flex inside the cabinet.

My gb142 went 17 winters , 3 cleanings , couple ignitors, couple pump accessory boards. Just overhauled in November 2025 with new heat exchanger, pumps and manifold. About $2500 of parts , cheaper than new boiler, plenty of spare parts on hand hopefully to keep it going another 17 years lol , I have a post about it here on the forum.