Buderus locking out after heat load changes

jgrear

I have a question about our brand new Buderus, which is in its second winter.  It has had one annual cleaning, but has now failed twice since that cleaning.  Installation, cleaning, and service has all been with one company.  Here are the details

We replaced our New York boiler in Oct 2023 with this Buderus Logano G115 and a Carlin EZ-1 burner.  It got thru the first winter just fine.  It was cleaned and serviced in Aug 2024.  On Jan 4, it locked out. The tech was here on Jan 6 and initially determined that the flame detector was faulty, based on the fact that it was showing high ohms (>1500) even when there was a flame present during a reset cycle.  He then decided it was the controller (Carlin 70200S), and replaced it with with a Resideo (R7284U1004), which is what he had in his truck.  It was still having problems, until he temporarily extended the ignition time and held a rag over the air intakes on the burner, apparently to heat up the flu, and then it ran just fine.  When I asked what would stop the flu and boiler from getting cold and air locked again, he adjusted the boiler temperature settings so it would cycle more frequently, admitting this would reduce efficiency.  

Here we are, 7 days later, and we have another lockout.  During my reset attempt, the ohms reading never got below 1600 during any of the three auto-cycles.  As I often do on the weekends, I had fired up our wood stove earlier in the day, so the thermostats probably hadn’t been calling for heat, but we’ve been washing clothes and taking showers, using hot water from the indirect water heater that was installed with the boiler.  

The boiler room is in a 10x12’ room in a large basement and has a louvered door.  The previous boiler and indirect water heater ran in there for 18 years with only annual service/cleaning and only two service calls. Our wood stove habits haven’t changed (i.e., occasional use for a couple days at a time).  The only thing that changed with the Buderas installation, aside from a beautiful rebuild of the circulator setup, was that they removed the Tee in the flu (which had a weighted adjustable damper).  The small boiler flu now just hooks up directly into the 6” insulated flu that goes up three flights to the roof (house built in mid 1990s).  

Can anyone suggest next steps? I’ve lost confidence in the service we’re getting from the people who installed the boiler (they don’t do service contracts).  I’m not even sure the $300 controller replacement (plus labor) accomplished anything.  Both failures occurred during weekends when we were burning wood in stove on the first floor , but the woodstove never caused problems with our previous boiler. Wondering if the change they made to the flu is the problem.

Thanks for reading this long email, and Happy New Year!!

Jason

HVACNUT

The starting point for us is to know the combustion numbers at steady state, along with smoke and draft readings. It's now 2025, and the only way to properly set up a burner.

GW

Jason, yes, it happens. He may have guessed, and it didn't go well. We've all been through it (dying for someone to disagree😊). Who is your oil supplier? That's normally the best route if you don't have a good independent guy. I do more Riello, so maybe some Carlin dudes can chime.

Wood stove——that can pull some air, and starve the burner (water heater call). I had to learn that the hard way years ago.

jgrear

Wow, thanks for the quick replies. I have the readings from the annual service in August. I'll give them below. But I have an update. I tried another reset, using a rag over the air inlet this time. The ohms reading dropped to 800-900. If I removed it, it jumped back to 1600+, so I held it there until the flame test passed and then the boiler ran smoothly. It brought itself back up to temperature, went into standby mode, and then failed again at the next call for heat. The wood stove had been out for a couple hours (and was never a problem with the old boiler; house is not supertight either), so I doubt competition for air is the issue. Also, flu airlock now seems unlikely, given that the restart is failing even when burner had only been in standby for an hour or so. I had to do the rag trick again. Here are the readings from the annual service in August. I'll type it the way it looks on the printout taped to the boiler:

8/22/2024

CO2max 15.7%

5.4% O2

10ppm CO

296.0 deg F. Fluegas temp

88.6% EFF

. ppm Ambient CO

73.7 deg F. Ambient Temp.

-0.066 inH20 Draft

32.4% Excess air

. inH20 Pressure

11.65% CO2

14 ppm Undiluted CO

Smoke no. - - -

Smoke no.0 -

HCT ________F

Jason

Jamie Hall

Shame that modern cars don't have hand chokes. If you can get it to fire by slightly reducing the air to the burner with your rag trick, this should tell you — and your service man — that there is a little too much air. Probably not much — the combustion numbers are at least reasonable — but just enough so that the poor thing can't fire off.

Sorry about the controller. I happen to think the Carlin 70200 is the best one out there…

HVACNUT

-.066 draft in the breach is too high. It should be -.02. Is there a draft regulator?

It's also got low stack temperature, so was the boiler at steady state when the readings were taken?

G115-? What nozzle is in the EZ-1? What's the pump pressure?

jgrear

There was a draft regulator with the old boiler, but they took it out when they installed the buderus. I could install one myself and then call service tech to adjust it and retest (BTW - I did notice a slight smell of partially burned diesel in the utility room a few hours before the first failure). I'll check nozzle size after work today. I don't have any way to measure pump pressure. For steady state testing, is it supposed to reach standby mode, and then forced to fire up before readings are taken? If so, I can only assume that's what they did.

HVACNUT

Steady state is when the boiler (burner) is running and the flue gas temperature has reached its maximum and stays there, within a few degrees + or -. Run all zones to maximum. Run the bathtub if needed.

The installers should know a regulator is needed and adjusted to manufacture specs. Have them do it. It should've been done with the job.

jgrear

Not going to try installing draft regulator myself, even if that's the problem. Got some nozzle and air band info and a correction on the flu size. Just hoping for some advice here so I can ask the current tech about it one more time before I try someone else.

Flu: It's actually a 5" with two elbows before side entry fof 7" flu, which actually goes straight up at least 40' (four flights; forgot about attic).

Nozzle: 0.60 065. The boiler is G115WS-3, so manual says it's supposed to be .60-60 (B or W) Delavan nozzle.

Air Band: It is set at 0.5. Manual says to use 0.60.

Stack Temp.: as mentioned it was 296F at summer cleaning time. Manual says it should be 390 - 440.

Do the deviations from the manual fall within the limits of what might be called "fine tuning"? Or could they be causing the flame/lockout problem? CAD is still oscillating between 1540 and 1630 during regular burn, and it drops a lot when I loosely block the air band with a rag.