Buderus GB142 gas valve

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jadnashua

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I've got a Buderus GB142 boiler. It was giving a 6A error code, and shutting down. This means it is not detecting that the burner fired. After checking both the ignitor and flame sensor, and finding the ignitor glowing, and (I did clean the flame sensor, but it didn't help), the only other thing other than the forced fan induction is the gas valve itself...so, while it was trying to go into an ignition cycle, I tapped it lightly with a ball-peen hammer and it lit up.

So, after all of that, would the next thing be to replace the (apparently sticky) gas valve? I don't think that there's any serviceable parts in it. It looks pretty straight forward (I do have the maintenance manual).

The thing is 11-years old, so it is out of warranty. I think I read that the newer gas valves also require a circuit board to be replaced to match its new characteristics. I can try to call them tomorrow, but was wondering if anyone had any other thoughts. Don't want to spend money I don't need to.

At least it's heating up and I should have hot water for a shower in the morning if it finishes, even if it doesn't want to fire up again on its own...the tank's big, and well insulated. This all became apparent that I had a problem when the shower wasn't as warm as it should be, and I couldn't change the temp with the control.

I thought that it was probably the ignitor, since they don't seem to last all that long, but this one is working. These things always seem to happen on the weekend, and being frugal, didn't want to call someone out. Luckily, my condo only has two outside walls, is well insulated, and the other walls to adjacent units kept the place decent, but without hot water. It wasn't all that cold for this time of the year, either (around freezing).
 

NY_Rob

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If that's a mod-con (Modulating Condensing) boiler... it uses a complex negative pressure gas valve that must be "tuned" once installed using a manometer and combustion analyzer. It's not a drop in replacement part, it needs to be adjusted to spec once installed.

FWIW- your gas valve might not be bad, it may just need an adjustment by someone with the proper test equipment and the service manual.
 

jadnashua

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Yes, it is a modcon. The thing has been in service for about 11-years, and this is the first time this has happened...do they change on their own? It's been about 24-hours, and it's turning on/off without issues, but I don't know enough about them to understand why it would not open, but after a slight (I didn't hit it hard at all), it started to work, and has continued for awhile.

The last time I called to have a cleaning/tuneup, there was a slight water leak. They quoted about $2500 to replace the heat exchanger. I tighten up the connecting bolts that hold it together and the leak stopped. Then, I cleaned it, but don't have the tools to double-check the burner.

FWIW, what looks like the adjustment screw on the valve has thread lock on it.
 

NY_Rob

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Along with regular maintenance as directed by the install/owners manual- A combustion analysis should be done every couple of years to ensure the CO and CO2 are in spec and the unit is burning efficiently. Once you have the correct equipment, it just takes a few min to adjust the gas valve to the correct settings. Without the combustion analyzer and manometer there is literally no way you can adjust the gas valve to spec, or even "ballpark" it. Don't even try. And yes, they do need adjustment over time.
 

jadnashua

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Well, the thing ran for 5-days without issue, and tonight, it came back with the 6A error. It appears that it doesn't completely shut the gas off all of the time all of the way, either. I think it's time for a new gas valve.
 

NY_Rob

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^ You may (or may not) need a new gas valve... but just to reiterate- it's not plug-n-play like some other boiler parts.
It needs to be installed and tuned/calibrated with a manometer and Combustion Analyzer. You can't tune it by eye or ear.
 

jadnashua

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Yes, I understand...I've been reading the installation manual. I read somewhere, but can't find it now, that there was a reference indicating when switching from the old style gas valve to the newer one, you also needed to change a circuit card. Do you have any insight on that? Sounds like it will just add to the overall cost of repair. FWIW, it's still running, but the first time this happened, it ran for almost a week before it stopped again. The other gas appliances all seem to be operating as normal, so I don't think it's a supply issue. Any decent, manometers that don't cost a fortune? Exhaust gas analyzers seem to be pretty pricy for an occasional user, but it appears a reasonable manometer doesn't have to cost many hundreds of dollars. Just don't have any experience about which ones are crap and which ones work well, long-term.
 

NY_Rob

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Sorry, I have no info regarding swapping out the board with a new gas valve... contact Buderus, they should be able to give you the info.
Maybe they had some issues and the only way to permanently fix the problem was to replace both parts?
There are a lot of HVAC tech's at heatinghelp.com, maybe post over there regarding the board/valve question.


I bought a $40 manometer online, I compared it to my HVAC guy's expensive one... they both read almost identical pressures. Of course it's not commercial grade, but for occasional consumer use it will work, and the important thing is the differential pressure not the system pressure.
https://www.amazon.com/Perfect-Prim...UTF8&qid=1520089004&sr=8-7&keywords=manometer

I got my combustion analyzer (UEI C20) used from ebay... then I had to spend another $99 to get it factory calibrated and re-certified.
They need to be calibrated and re-certified every 1-2yrs.
 
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jadnashua

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Okay, I put a new gas valve in, adjusted the pressure per the manual, but the CO levels are huge, and don't seem to be dropping. At least the thing runs and doesn't shut itself down. After working for a few days after the gas valve, the ignitor failed, but a new one has been working.

So, I have a fairly accurate CO detector that I bought to use in an airplane (certified sensor) but it maxes out.

Basic, related question, how does a closed combustion system end up raising the CO levels in the house? I shut it off, and it dropped from about 8-9ppm in the house down to 1 right now, which is probably not an issue (well, even 9, while not great, isn't catastrophic). I wanted to verify that it was my unit (in the condo) that was raising the CO level, and at least empirically, that seems to be the case...turn it off, it drops.

The acceptable range of the after gas valve pressure caused by the gas valve and the induction fan is from 0 to -0.04, and I had it at -0.02, but raised it to -0.03 just before I shut things off to test the level dropped. I may leave it off overnight, as the house is well insulated, so it shouldn't cool off all that much, and the indirect will provide more than enough water for my morning bath. I'll turn it back on in the morning and see what the CO levels are.

Again, though, with a sealed combustion system, how is that exhaust CO getting into the dwelling? Thoughts?
 

NY_Rob

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"Sealed combustion" is sealed... nothing should be working it's way back into your home.
Either you have infiltration from your outdoor venting, or you have an exhaust leak from the boiler.
Could be in the exhaust piping, a bad heat exchanger gasket, dirty heat exchanger, etc...
Take a look a the link I posted below, that kit has a sniffer attachment- it pinpointed the exhaust leak my old boiler had before I replaced it with the mod-con.
When I hold my Sensorcon Inspector near/around my boiler it never changes from ambient (which is generally zero ppm CO)

You really need to get the CO level right before going any further.
What is "huge" CO reading you're seeing in the exhaust venting?

Without a (calibrated) Combustion Analyzer your readings may be suspect too....
 
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NY_Rob

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How long were you running the boiler for when you saw 9 PPM CO on your CO detector?

Was the detector in the same room as the boiler?

Could be potentially lethal situation.. make sure your household CO alarms are working and with fresh batteries.
 

jadnashua

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The ambient levels varied between 5-8ppm, but were not higher in the area of the boiler. I checked the outside termination to make sure it wasn’t blocked. It took about three hours after turning the boiler off for the ambient to drop to zero. I’m going to sniff around in a bit when I turn it back on. Last time I cleaned it, the bottom gasket didn’t look great, but it wasn’t leaking condensate, but I ordered a new one for the next time it was apart. No condensate leaks, so I figured it was tight enough for exhaust as well.

There’s a Nest protect co/smoke detector in that room and it hasn’t complained.

Annoying, but I’ll figure it out. The condo only cooled off about five degrees in the last 12 hours or so.

Took things further apart, and there's a crack in the inlet neck of the condensate bottle. I'll order a new one, but in the meantime, I'm going to put some foil tape around that to try to seal it up and see if that resolves the CO leak. With the forced fan induction of the burner, it will force gas out any hole. It was coming from the back of the system, but I didn't check the plastic condensate bottle (it's not that easy to access when everything is together). The crack is on the back side of it next to the case, so it wasn't visible until you take it out. Because of the angle, it wouldn't leak condensate, but could easily let flue gas escape. It was dirty, so I decided to take it out to rinse it out which is when I found the crack. I'll replace that lower seal while it's apart, but I don't think that was (also) part of the problem, but it is looking a bit worn. The upper seal looks good.
 
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