Boiler Running Full Tilt, Cold House

Dan Foley · February 17

I have had this happen on a Viessmann several years ago. It would run but appeared to be locked in low fire. I found a partially clogged intake screen on the gas valve. I cleaned the screen and the boiler then ramped up to high fire.

EBEBRATT-Ed · February 17

8.5 Co2 lean?

You have to be kidding. 1/2% Co2 is not going to cause an issue. Fuel temp changes air temp changes You can't stop that from happening.

You don't set up any boiler for an exact # and have it stay that way

GroundUp · February 17

Yes, 8.5 is too lean for this particular boiler. They run a whole lot better and cleaner at about 9.2%. And yes I do set them for an exact number, as does every other professional. These Nobles are incredibly picky. Is it causing the issue in question? No. But it is still a problem that needs to be corrected.

Teemok · February 17

Tune has little to do with the size of the experienced, clocked and calculated BTU deficit. It’s not an ignition or flame stability problem, even if it’s a bit lean. I can’t find the right manual. Maybe you guys can.

mattmia2 · February 18

i linked the manual for a nobel of that type about 10 comments back, not 100% certain it is that exact model.

Teemok · February 18

I’m not either. The vent port locations are not the same as shown in the manual. I’d bet the gas train is similar but guesses aren’t very useful as a reference.

hot_rod · February 18

Well Alan sure has his work cut out for him with all the good suggestions.

Jamie Hall · February 18

All this is fascinating… you would think that there would be a mass airflow sensor controlling the gas flow… apparently not? I'll grant that they aren't really cheap — a few hundred for OEM ones (don't use anything else!) but… there aren't all that many gasoline powered cars out there today that don't use them!

hot_rod · February 18

https://forum.heatinghelp.com/discussion/comment/1843293#Comment_1843293

Burnham and Viessmann have boilers with adaptive gas valve control, maybe with more sophisticated gas valve control ?

IMG_9709.png

Teemok · February 18

Better learn to test stepper motor gas valves. Measuring flame ionization becomes a weak link. A dirty flame rod signal feeds junk info to the control. That said, I’ve not played with any beyond watching them work well on start up. Always stuff to learn.

Teemok · February 18

A boiler with an adaptive gas valve still modulates on fan speed. An air restriction case is still a BTU production limiter; though, it might be in better tune while it’s hobbled. New Baxi is adaptive, I think. Adaptive is a good step forward. Gas conversion is programing and variances in conditions and installation are self managed. This makes them better suited for hang it, pipe it, walk away types. When things do go wrong, maybe less than before, It’s the same type of set up, a bit more complex. Maintenance and a skilled tech are still key. Rebreathing and flue installation problems will still be common.

Alan (California Radiant) Forbes · February 18

I had a Viessmann "No Heat" call in Jamestown yesterday - two hours away, off the grid, propane - that took most of the day away, but I'll have time today to visit this job. I plan to test the gas pressure at the boiler and remove the air intake pipe to see if that reveals anything.

I don't have the correct adapter to check the gas pressure at the meter, though. I've seen the utility guy do it with a cone shaped adapter that he shoves into the meter outlet.

BTW, the meter is about 10 feet away from the boiler.

Alan (California Radiant) Forbes · February 18

The natural gas pressure reads 7.40”static, 7.23” dynamic which is not much of a drop and lends itself to a problem downstream.
I adjusted the gas mix to 9.2% CO2.
And I removed the air intake pipe to check the shutter. It moved only slightly, but I think it’s made that way. The opening to the Venturi is dirty, so an inspection the HX is indicated.
Lochinvar tech. support discounts the low BTU usage reading that I got when I did the clocking at the gas meter. He said it was probably an error and that a thorough cleaning of the gas side of the HX is necessary along with replacing both the inlet and outlet sensors which should be replaced every time it’s cleaned.
I’ll do as he says, not because I think he’s right, but I want to inspect the gas valve, fan and combustion chamber. I’ll order the sensors and maybe even a gas valve.

mattmia2 · February 18

what does the index on the meter say: 7"wc? it will under read a little bit at 7.25" but not 40%

Did you see what the blades of the blower looked like?

Teemok · February 19

Dirty ; Venturi, fan, THE BURNER, heat exchanger. A cumulative effect? Venturi work on velocity induced pressure differences. Dust/ debris in just the right spot could change things, maybe. Look for a cleaner source of combustion air or a way to prevent the current contamination. HX sensor replacement for no reason? Either they are a known problem or it’s a tech support “up sale” or just silly. The sensors are testable and the symptoms aren’t related. Cleaning the fire side HX has nothing to do with them. Are they suggesting you acid clean the water side and that’s why you are to replace sensors? Pull, plug and re fit would work too.

mattmia2 · February 19

Perhaps they don't sell the o-rings for the sensors as a separate part? bmw coolant temp sensors are like that so you have to find the size and buy an o-ring when you replace the lower radiator hose.

hot_rod · February 19

When was it last opened up and cleaned?

Teemok · February 19

Typically they are threaded. Lochinvar won’t sell you a flue sensor grommet either. You must buy a sensor “kit”. The bean counters know where profit comes from.

Alan (California Radiant) Forbes · February 19

I haven't opened up the HX yet and it's never been serviced; 5 years old. The local utility company is coming out on Friday to check the regulator at the meter and I've ordered a new gas valve and sensors which should arrive this week.

GroundUp · February 19

Judging by the look of the venturi, the burner is probably filthy. Possibly so bad that it's unable to be cleaned. That would certainly play a role in the actual airflow here, causing some or all of the symptoms you're seeing. I would agree that the temp sensor replacement is unnecessary, but I'd order a new burner and fan as well before you go back. Did you adjust to 9.2% at high fire or low fire? Using the bias or the throttle screw?

mattmia2 · February 19

i didn't think about the burner being essentially a screen, that could certainly clog up to reduce airflow by 50% ish.

is the intake near a dryer vent?

hot_rod · February 19

You never know what you might find when you dig into a boiler that hasn't been services occasionally. This boiler wasstill operating!

Screenshot 2025-02-19 at 12.41.45 PM.png

Teemok · February 19

Not sure why the gas work is being done when you proved it to not be a problem. Burners can be very easy to blow out with compressed air depending on the contamination. Working fans and Venturi are easy enough to clean well if undamaged. New parts are sure and easy but costly. I never believe tossing parts at it is wise. Do enough at once and you won’t know what the problem was. Having parts on hand might be wise if the drive is long but doing maintenance, cleaning and investigation into why it’s that dirty and changing that would be my approach. That said you know more about the case and may have good reasons to do other things. Replacing the boiler would 100% fix the problem, I don’t recommend that.

mattmia2 · February 19

https://forum.heatinghelp.com/discussion/comment/1843628#Comment_1843628

i'm afraid to ask what that is.

mattmia2 · February 19

https://forum.heatinghelp.com/discussion/comment/1843632#Comment_1843632

i think he just wants to make one more trip and doesn't want to get inside it and find out he doesn't have a part he needs but needs to get it running at least the way it is now somehow. but i do agree that it isn't the gas. also 1" wc isn't going to make a huge difference in the clocking because the absolute pressure is something like 120" wc so the ratio of the volume isn't changing much.

Teemok · February 19

I have done this and seen others go through the process before. Investigation, test, theorize, careful investigation again, analyze, test other things, get soooo close ……. and bang! The parts cannon is fired. It is fixed after that, most of the time. What did we learn? The parts cannon worked in this case. What really fixed it? **** if I know.

I’m sure Alan will be looking for something that is the most likely cause when trying to eliminate the problem (his main task). From my comfy perch, I can prioritize learning over fixing. I’ve been there. “I must fix it this visit ” Not judging.

mattmia2 · February 19

i;m sure he isn't planning on replacing all of them, he just wants to have them on hand

Teemok · February 19

Right, I got that. I said that is wise.

hot_rod · February 19

its a good idea to have a top end gasket kit if you tear into it

hot_rod · February 19

https://forum.heatinghelp.com/discussion/comment/1843652#Comment_1843652

flys of some sort

Alan (California Radiant) Forbes · February 19

Lochinvar tech. support has been helpful…..to a point. You get to know which ones will listen to you and which ones spew kvatch and have you barking up the wrong tree. But I didn’t see any harm in having the utility company check or replace the gas regulator as I’ve often taken a wrong turn on the troubleshooting flowchart.
The Lochinvar guy said he’d never heard of a torn diaphragm or bad solenoid on a gas valve, but I want one there if everything else looks good. I’ve never seen a badly clogged burner, but @GroundUp adds that possibility as that can certainly impede air flow although, now that I think about it, there was good suction at the Venturi. And yes, I adjusted combustion to 9.20% CO2.
The exhaust/makeup air vent via a roof concentric and the dryer vent is vented out the side; not close enough to be a problem.
I feel very sorry for the owner as she is very sick and is miserable with the cold floors. She has been very patient and has said that I should just replace the damn thing. I just can’t bring myself to do that ……..yet.

GroundUp · February 19

@Alan (California Radiant) Forbes yes you mentioned that you adjusted it to 9.2%, but I asked if that was at low fire or high fire and which screw you used to do it. One screw is to be adjusted only at low fire, and the other screw is to be adjusted only at high fire. If you adjusted the low fire screw far enough to raise the high fire reading by .7%, you've created bigger problems. I just wanted to clarify what exactly was adjusted and how. Seeing as it's a concentric vent (big no-no with a Noble), I wouldn't have any trouble believing the burner is plugged or even ruined- I see this more often than not with concentrics. Perhaps a couple feet could be added to the exhaust side of the vent to further separate it from the intake?

mattmia2 · February 20

i'm guessing @Alan (California Radiant) Forbes is getting paid in experience on this one.

hot_rod · February 20

I think you will see a lot when you take the top off. Burner tube condition, damper, insect build up, fire tube condition,etc.

In Missouri fireflies tend to get sucked in the intake, something about that pvc or noise attracted them.

I think concentric vents doom many a mod con

Teemok · February 20

Where is that dirt from? I have burners sucking close to roads and I don’t see that much in the Venturi. Is there an exhaust fan near or a central vac. System. I cleaned a burners that, when i blew it out, I was surprised by what was in there. I thought, it must have been limiting full output. It was oversized enough that no one noticed any reduction. Remember old Occam’s razor. The simplest explanation is usually the best. Dirt simple.

mattmia2 · February 20

maybe a cottonwood and that got mixed with dirt in the air?

in our projectors in our classrooms we see almost nothing in most of the filters except in projectors that are near inpatient areas of the hospital and in those we see stuff like what is on that flapper. we had one that would get blocked every couple months. i'm pretty sure the stuff comes from the linens.

mattmia2 · February 20

just thought of something else. make sure the intake side isn't broken somewhere and sucking in cellulose insulation from some cavity

Alan (California Radiant) Forbes · February 20

@GroundUp The 9.2% was at high fire; adjusted with the throttle screw. I won't **** around with low fire adjustments until we get this figured out.

I also want to check and see what the gas pressure is to the manifold before I take it apart. Just to see if that gives me any information for future troubleshooting.

@mattmia2 The concentric vent daylights on the roof with nothing obvious around that would slough off into the boiler's intake. It's pretty damn clean. The debris on the venturi is a mystery.

mattmia2 · February 20

or maybe someone was installing or removing insulation in the area and it got sucked in by the boiler. When I zoom in it really looks like the cellulose in my house where it squirted out gaps as it was installed.

Boiler Running Full Tilt, Cold House

Comments

Categories