Lead Boiler shut-down: cause?

vaporvac

Oh thank you, @Jamie Hall . I hope nobody thinks I'm being all "know-it-all" regarding the controls and am totally open to other ways of doing things. That's how I ended up with this system after all! I really thought it would only be vstats control myself when originally conceiving this system until I saw some of the twinned installs and inquired about the nuts and bolts of the controls We were able to hook up the tstat without help as originally, I had to manually shut them on and off! I'm trying to forget those days, I was just happy to have heat. Doing the vsats stymied me. I think the tech left me a diagram last year. He also drew out very good instructions for both ends of the two-staged Tstat should I decide to do that myself (which I think I'll at least try.)

Pretend you now hear a drumroll..... I think it's fixed!!! I want to thank EVERYONE who has responded because I've now learned how to use a multi-meter, clean my vstats and set them and clean the probes and change the wiring on it without being too scared AND clock the meter! I also learned about the burner reset, what a snubber does and discovered a small gas leak which we fixed this afternoon. Old union after the shut-off....how did that happen?
The culprit was a break in the wire from the Taco to the lead boiler Vstat. We fixed it, albeit temporarily, and it's been running for quite sometime without issue. Keep your fingers crossed.

(I'm going to re-clock the meter again and see If duplicate the first numbers. We have high pressure gas so there's a regulator coming into the house and also at the boilers. Maybe the tech changed it? I know my numbers are super,) Whew!
Colleen

BobC

Glad to hear you got to the bottom of it. Sometimes you just have to keep turning over rocks till you turn over the right rock.

Bob

Fred

That's great @vaporvac !

vaporvac

I am going to reclock the meter to verify those numbers. It could be I'm not getting enough pressure, but that doesn't seem to be what was shutting the boiler down... definitely the wiring as it transferred the problem to the lag Vstat when I switched it. I got a nice long uninterrupted firing once the wire was fixed. While I understand why it didn't work, I don't understand how it ever did . Why did the multimeter register continuity? Why did it work sometimes?

Jamie Hall

Hooray!!!!!

SWEI

Hatterasguy said:

A multimeter will register continuity if a microscopic strand of copper is present.

This does not mean the circuit will actually perform as the resistance to current flow is huge with a minimal conductor. It will also likely warm itself quite a bit.

True for a resistance measurement, which is why we usually measure voltage, looking for drop along the path.

ChrisJ

I very often do a simple continuity check, you know, the kind where the meter beeps? I'd call that good when seeing if a vaporstat was open or closed.

Sometimes I'll use an ohm meter, sometimes I look for voltage drop. It all depends on what exactly I'm looking for or trying to do.

There are times I'll fire a piece of equipment up and start twisting and bending PCBs trying to hunt down a cold solder joint. Same goes with wires, pull, bend twist etc.

Intermittent problems suck to troubleshoot and unfortunately I'd say they are the most common and the only thing that will make it easier is practice.

vaporvac

That certainly sums it up. I still need to replace the wire as it still work intermittently, but at least now I know the reason. I still don't understand why it will work fine if only that boiler is running. That makes no sense to me.

Fred

If that wire were the only issue @vaporvac , it would be an issue running alone or in combination with the lag boiler. I keep saying the gas pressure is an issue when both boilers are running. Do have that checked out.

vaporvac

Thank you @fred. I will do that. Just wondering out loud. It's also strange that after the boilers start chugging away, the issue disappears. it's only that way for a while.

Fred

Huh, maybe there is a sudden pressure drop when both boilers kick in and the regulator out by your gas meter adjusts for it but just not fast enough for it to be transparent to the boilers. If it turns out to be something like that, i'm sure the pressure can be adjusted slightly upward or the boiler regulators adjusted slightly downward to compensate. It is so strange that you didn't experience this problem before this year???

BobC

Old incoming gas pipe corrosion?

Get someone to measure the pressure drop when the boilers and any other gas appliance are all firing.

Bob

vaporvac

They ran like clockwork until this year. @BobC , how would we measure that exactly? I may be able to do that tomorrow after we replace the faulty wire.

BobC

You need a manometer. Put it at the input of the boilers gas valve and then turn on both boilers (and all the other gas fired appliances) and see how much it drops. If it drops to 5" or less you have a supply problem.

Then check the pressure at the output of each boilers gas valve to what this doing with both boilers firing and then with all other gas appliances running (water heater, stove, etc).

This has to be done by someone who is licensed to work on gas equipment.

Bob

vaporvac

You all thought I had this fixed, right? Well, I just wanted to make some progress before posting. In any case, my above conclusion was wrong due to poor logic and coincidence.

vaporvac said:

I then disconnected the Vstat wiring to one boiler at a time, as mentioned above, which completely shut off the boiler and the red light at the Relay. Then I switched the Vstat wiring from the lead to the lag and vice-versa. That switched the ON/OFF problem to the lag boiler, so what is that telling us? The problem is in the relay? The wiring itself seems to be fine.

I assumed it was the wire since it was spliced, but in a head-smacking, eureka, I am an idiot moment, I realized what this meant: the problem was the Vstat. I replaced the wire anyway and the problem continued, as expected. I then permanently jumped the Vstat wiring with a wirenut to keep the boiler on without the Vstat attached. It then ran perfectly... for days now. Without a hiccup. It was the Vstat, after all. It runs at 11oz. with both boilers and after it's hot it drops to nothing and then goes into a vacuum. (This probably explains why I had no problems initially until some pressure built, and then it would go back to working as pressure fell.) I manually shut off one boiler if I'm home, when the temp is within 1 or two degrees of set and it coasts right up quickly, and the rads stay hot for a couple of hours.



So onto the Vstat issue. After rewiring, I tried to trip the Vstat....nothing until I touched the differential and it started tripping the Taco Relay on/off, on/off. Not long enough to shut off the burners, but rapid fire. @Jamie Hall has written that the old mercury vstats need to be level. Mine is way out of level. What problems would an out-of-level vstat exhibit? I'm going to work on it Friday and see if that fixes anything.
What else can go wrong with a mercury Vstat? It worked great on my old boiler. This is the type that one changes by turning a screw in the middle with the differential on a wheel at the top. It goes 0-160z and has a max 4oz differential. Opens on rise. Maybe I'm setting it wrong. I never had to change it before. I probably don't need it as @nicholas bonham-carter mentioned, but I'd still like it to work.

Also, anyone have any thoughts on settings for my lag boiler?

ChrisJ

If the unit is out of level it can cause issues with how the mercury switch operates. If you watch how the mercury flows in the bulb you'll understand. I suspect slight out of level won't matter, but I've never done any tests my self. I'd just do what I had to, to make it level. My older Pressuretrol even has a metal arrow hanging in the back inside to assist in this without an actual bubble level.

My first thought is I wonder if the pigtail is causing issues like I saw with mine. I saw all kinds of problems using a pigtail at low pressures which is why I eliminated it on the stuff I use to control things. I still have it on my code required 30 PSI gauge and Pressuretrol, but my Dwyer switch and Magnehelic are connected to an 18" long vertical 1/2" nipple and it works far better. I needed to use a 0.015" snubber from Mcmaster though.

The long nipple acts as an air trap so steam can't get to anything as long as nothing leaks. If something leaks then the control and gauge are toast. So far, I've had zero problems.

What I saw from a pigtail was mainly over time, a vacuum would develop between the pigtail and the gauge / control. This doesn't happen with my setup.

Jamie Hall

If this is the old style mercury vapourstat...

There are two settings: the cutout, which is the right hand scale and the screw on the right at the top, and the differential, which is subtractive, and is the screw on top on the left.

You will either need a sensitive pressure gauge (or a Hoffman Differential Loop! but using that takes a good bit of patience!). What you need to do is set the cutout for some reasonable -- but achievable -- pressure. Then let the boiler fire, and keep an eye on the mercury bubble. As the pressure rises, the mercury tube will very gradually start to tip to the horizontal. The objective of the exercise is to tip the whole vapourstat so that when the pressure gauge shows the pressure you want to cut out at, the mercury blob in the tube is just about to slide to the left end of the tube. This is what breaks the circuit and opens on rise. It's a little fiddly until you get the hang of it, and it assumes that the pigtail connection to the header has just enough give in it to let you do this -- but not so loose as to lose the setting once you've done it.

The vapourstat case should be pretty close to exactly level when the tube tips to the left, but it may be a little off. If it's a lot off, then there's something wrong with the diaphragm in the vapourstat, or with the connection to the boiler or header.

That tip over point is very sensitive. If there is much pressure jitter, you may find that you can't get a consistent setting, and that is why I have a snubber on mine!

Once you get that set, the differential should be fine; keep an eye on that mercury tube as the pressure drops, and it should tip back at the cutin (which is the cutout you just set, minus the differential). Also, once you have the level set, you should be able to adjust the cutout to what you want, if that isn't what you had it set at for this little exercise in precision leveling.

Fred

WOW, @vaporvac ! At least now you know where the problem lies. Good work!

vaporvac

Wow guys, great instructions. I'll post a pic of my set-up when I get home. It's on the header like so many of Jstar's and I think @Jamie Hall 's. No pigtail as the hoizontal pipe takes the place. The gauges are set high above that. The horizontal never gets hot, but I worry since it overfilled last year. However, it's not exactly hizontal shich is part of the problem perhaps.

My "broken" Vstat is a mercury type, I presume because it's probably from the 60s. It's a White-Rodgers, but there's no way to see the mercury bulb as in the Honeywell model. I only see the main with a screw in the middle to change the setting and a small wheel/dial on top for the differential. Moving the small wheel is what cause the rapid fire tripping at the Relay. Changing the main setting did nothing. This vertical arrangement is attached to an enclosed round box that I assume houses the mercury bulb. I've never opened it.
I'll be spending some time on this tomorrow; the vertical attachment from the horizontal pipe seemss a bit off just looking at it.

Thanks for this feedback. Yes, I'm glad to know what was the definitive issue. I literally stopped in the middle of the street during my run, slapped my forehead, and said "I am an idiot!", probably really loudly because I wear headsets. The look on my neighbor's faces told me they agreed!
Colleen

vaporvac

I don't have a pic of the completed set-up. This shows the horizontal bar coming down from the header. The Vstats & vacuum gauge come off of it rising about a 8-12".

ratio

Maybe it's time for a new vaporstat? I'm not a fan of repairing defective controls when a replacement is only a few hundred.

That said, I haven't been able to adjust the differential on my brand-new vaporstat to less than about 8 oz, the spring starts to lift at that point. It's about what I want, or I'd've taken it back.

ChrisJ

ratio said:

Maybe it's time for a new vaporstat? I'm not a fan of repairing defective controls when a replacement is only a few hundred.

That said, I haven't been able to adjust the differential on my brand-new vaporstat to less than about 8 oz, the spring starts to lift at that point. It's about what I want, or I'd've taken it back.

Switch to Dwyer switches. My lowest pressure switch maxes out at 2 ounces and can be adjusted down to practically nothing. You'll need to build a @MarkS "Dwyerstat" though. I think it requires two of the switches and a simple relay setup.

ratio

I actually had one, but I must have gotten steam into the cutout switch, as she didn't when I started her up for the season.

I ended up replacing the old pressuretrol with a 4 lb vaporstat since I run at 1 lb. If I ran at vapor pressures I would have repaired the Dwyerstat.

vaporvac

Hey all and Happy Merry!!! I'm sure everyone thought (if they thought about it at all), that this problem was resolved after my last post....well, not even CLOSE! This is a case of how many things can be slightly off, but now it is definitively fixed.

The old White-Rodgers mercury Vstat DID need adjusting and setting plumb. That stopped the rapid-fire on/off, bit the lead boiler still went off at exactly 10oz. as before. However, I could never get it to trip manually, so I think it's toast. I then cleaned the Ptrols and even switched them to the opposite boiler and it still went off even when i jumped out the Vstat.

So I moved on to the gas meter suggestion. A super nice, smart guy from Duke come out after clocking the meter showed anomalies. However, my incoming pressures and volume were all great, so that eliminated that as an issue. Then I spoke to the helpful people at Riello. They suggested it could be a gas piping issue (not) or a pressure into the burner issue, something that calls for a tech, which I did.

I really like these folks I found to service my boiler. He had to come out twice, as he was also stymied. However, the first visit near the end of the call I mentioned about the Taco light going off to the problem boiler. He looked at me with that, "Why didn't you say that in the first place" expression and went on to explain that THAT completely eliminated the burner from the equation. It had to be a control issue. Finally getting somewhere. He jumped out both the Prol and Vstat and told me to report back after I fired it up again the next day. (It only reaches the 10oz from a cold start.) He also readjusted the Vstat and Ptrol on the lag boiler down.

In discussing the Taco wiring, he mentioned that Relay 1 was the lead boiler which got me thinking, as I always thought Relay 2 was the lead. Well, the next day it the lead STILL WENT OFF, but at 2 oz!!!! AND, it was the Relay 2 light that went out. So I knew then that the burners were wired to the wrong controls!!!!! and adjusting the Vstat/Ptrol on the Lag boiler had lowered the set-point for the Lead boiler!!! Can you see why I've had such a problem troubleshooting this?
(OK folks, I did not do this wiring. It was professionally done.)
Matt , the tech, didn't believe it as he had checked it, but only for the safety wiring and assuming Relay1 was the lead. However, it was mis-wired. On top of that the new Vstat is so out of calibration I may just investigate a Dwyer switch at some point. It cuts out at 1-2oz when I have it set for 15oz! (I couldn't find a post about trying to re-calibrate it if that's possible.)
So now my boilers are just running on the Ptrols as a high limit, although they only reaching about 1 lb. I'll get the two-stage Tstat wired here soon to get some auto-staging and then investigate pressure limiting options for the lag boiler.

Is everyone confused yet? We still couldn't figure out why my burn rate is what it is, but I have great efficiency numbers 87%+.

Whew! I'm just glad it's solved.

ratio

Sometimes it's faster to just rip out the old controls & redo it than to go through & find the problem. Glad you got the issue taken care of, even if it sounds like you've got another to look into.

Merry Christmas!

nicholas bonham-carter

Glad you solved the problem!
Why is the Taco relay box necessary?--NBC

hvacfreak2

To isolate the control power supplies for the 2 boilers ?

nicholas bonham-carter

Well it certainly did a splendid job of isolation!--NBC