Lead Boiler shut-down: cause?

ratio

With the system operating, you should see no voltage with the meter leads on the terminals where the wires are when the contacts are closed, that is, firing. When the contacts open, that is, not firing, you'll see the control voltage across the two terminals. And, as mentioned earlier, a jumper should turn the corresponding boiler on, if it's off due to pressure.

vaporvac

I assume they were correctly set up originally as they were done by a pro from this board. I don't know if the tech changed anything when he was here last week and the one burner's vent had closed.
I'm disconnecting the lead Vstat while both boilers are on to see if it runs OK.

ratio

If I have the right picture in my mind, if you disconnect the wire from the vstat, the corresponding boiler should shut down; conversely, if you jump it out the corresponding boiler should fire.

If you have them both jumped out they should both be running. If that's not the case, some other control device is in play.

Fred

ratio said:

If I have the right picture in my mind, if you disconnect the wire from the vstat, the corresponding boiler should shut down; conversely, if you jump it out the corresponding boiler should fire.

If you have them both jumped out they should both be running. If that's not the case, some other control device is in play.

Assumming there is a call for heat. The other control in play is the thermostat. I still think the issue is gas supply, I'm just sayin

vaporvac

OK. I may have alot of downfiring going on ,but the numbers were good last week. However, when I shut off my little ball valve leading to the lead Vstat, the boiler stayed on. So, it looks like the Vstat is the culprit. However, as both Vstats seem to be "bad" shy is only the lead boiler going off? What should I do now, besides see if there's some debris there, try and calibrate them and add a snubber?

BobC

Sometimes the little orifice at the base of a vaporstat gets clogged, it would be worth unwiring it and taking the vaporstat off to inspect it. While it's off verify the pigtail under it is clear and free.

What is each vaporstat set at? Before trying to calibrate anything I would just adjust it up to see if that affects the operation.

Bob

Fred

Shutting off the ball valve to the Vstas won't shut the boilers down. Closing that ball valve just takes the vstats out of the equation. With the ball valve closed, you have isolated the vstats and They will not see pressure so they could never shut the boiler down.
Also, the likelihood that both vstats are bad, at the same time is not likely at all!

vaporvac

@fred. Yes, that's correct. I wanted to take the lead vstat out of the equation and see if the boiler stayed ON without it. It did, so I'm thinking it's the Vstat that making the boiler go off. p.s. I did raise the setting alot and that didn't change a thing.

ratio

Fred, your right, it could easily be a gas supply issue, especially if it only exhibits when both are firing. But I'm a controls guy, so I have to look at those first. Also, my complaining to plumbers about gas piping usually falls on deaf ears. Apparently I like to size my gas lines ...generously...

vaporvac, to remove the vstat from the equation you need to jump it out, across the terminals, that will "remove" the contacts from the controls & pass the signal on to the next device. Closing the valve will isolate it from the boiler pressure, but without additional valving & work it'll just see whatever pressure happened to be at the vstat when it was isolated - high or low.

nicholas bonham-carter

Closing off the line to the vapor stats does not really help to isolate the cause, if it is electrical.
Perform the jumper-diagnostics one group at a time, and see if both boilers continue firing:
1. All vapor stats.
2. All LWCO's
3. Flue dampers
4. Taco switching device.
If the burners fire reliablely, then you can presume the fault lies in the safeties, or the Taco switching device. Watch the water lines while testing the LWCO's.
Otherwise, you are shooting in the dark.--NBC

Jamie Hall

NBC is right -- no surprise! Allow me, however, to add a bit: do it very very very systematically. I have a suspicion that you do indeed have two problems, but you need to clear the controls first.

vaporvac

Question: If the gas were truly the culprit, why would the two boilers run without issue, when I shut off the lead Vstat?

Fred

So many variables. When you say you shut off the vstat, did you do so as other have suggested by jumpering across the terminals? I wouldn't think they would both run fine if gas were the issue but we don't know if the gas supply pressure is constant or fluctuates. You might want to try switching the vstats between boilers and see if the problem moves to the lag boiler. Do go through all the control testing as has been suggested by others and reclock you gas after that. The clocking you had in your earlier post is also reason to double check what is going on there.
It also seems strange to me that the boiler runs fine when it's running by itself, if the problem were the vstat.

vaporvac

No, I'm not home. I'm referring to shutting off the ball valve that lets it see pressure. I did that last night to have some heat. Otherwise it was taking hours. I jumpered when they were running yesterday and it seemed to indicate there were issues with BOTH Vstats which seems unlikely since only the lead boiler is shutting down. It could have been user error. You must all feel like reaching across the monitor and shaking me. Unfortunately the multimeter left with my friend, but I can still try jumping everything AGAIN when I'm home. I'll update if both boiler are still running fine with the lead Vstat shut off.
I'm going back down to jump whatever else I can manage.

Fred

Is your cut-out pressure, on your lead boiler, set high enough that that vstat doesn't trip when the lag boiler is also running? I assume the lag boiler drops out at a lower pressure than the lead boiler or visa versa?

vaporvac

Yes, I reset it to 24oz... I'm only showing about at at the vacugauge and my two pressure gauges. The lag is set lower and should drop out first, but since I don't reach a high enough pressure it keeps running. I haven't tried to lower it until it trips. Historically, even from a cold start, I've rarely seen more than 1lb of pressure on either boiler.

vaporvac

New result. Yesterday the boilers ran fine after shutting off the ballvalve to the lead Vstat. However, they started up normally, but then the lead shut off and didn't turn back on. I reactivated the Vstat.... nothing. Then I jumped it and, voila!, it started up and went back to doing the crazy on/off thing. somehow I feel the answer lies with the Taco relay.... why does the red light go off when the lead shuts down, but if it's running and I manually shut the boiler switch off the boiler, the Taco stays red.
I'm going back down to jump whatever I can manage.

BobC

Do you have a diagram of the wiring between the relay and the boilers?

If not can you get one from whoever wired it up for you?

Bob

vaporvac

@BobC , this is what I have from the Taco site. I don't have zones hooked up from the tstat yet. I tried taking a pic, but it was too low res to see.
http://www.taco-hvac.com/images/100-88.pdf

Since jumping, the red light stays on at the Taco relay, recognizing the call for heat.

BobC

With the red light on I assume the boiler stays running? Have you removed the vstat and verified it's base is clean and the pigtail is clear?

It could be a bad vstat, you could try swapping them as someone suggested earlier.

Bob

BobC

It looks like the led is confirming there is power on the device it's connected to (safeties are ok). It's only the lead boiler LED that goes out when you remove the jumper?

Bob

BobC

This post shows what kind of crud can accumulate in a pigtail and ptrol/vstat

http://forum.heatinghelp.com/discussion/156055/single-pipe-steam-that-mostly-works-but-im-here-arent-i#latest

Bob

ratio

Don't keep us in suspense...

vaporvac

I won't leave you hanging; I was playing hooky today. I'm back on the job tomorrow and will continue with the saga. I'm going to clean out and switch the vstarts to start and see where that gets me as it's probably a good thing to do anyway. Thanks.

nicholas bonham-carter

What is the purpose of the taco switcher?
I think you only need one vaporstat to shut off the lag boiler when the pressure rises to a few ounces. When the lead boiler is firing on its own, the pressure could not rise, but instead will become sub-atmospheric.
This is where the 2-stage thermostat comes into play, as it will fire the lead boiler only until the room temperature has dropped a degree or two, and then will fire the lag.
Don't forget our advice, so you are not shooting in the dark.
As far as the source of the problem, my bet is on the Taco switcher, which would not be needed with the 2-stage thermostat, in any case.--NBC

ChrisJ

nicholas bonham-carter said:

What is the purpose of the taco switcher?
I think you only need one vaporstat to shut off the lag boiler when the pressure rises to a few ounces. When the lead boiler is firing on its own, the pressure could not rise, but instead will become sub-atmospheric.
This is where the 2-stage thermostat comes into play, as it will fire the lead boiler only until the room temperature has dropped a degree or two, and then will fire the lag.
Don't forget our advice, so you are not shooting in the dark.
As far as the source of the problem, my bet is on the Taco switcher, which would not be needed with the 2-stage thermostat, in any case.--NBC

Can you give some examples of a 2 stage thermostat? Models etc?

SWEI

Too many to list -- all of the manufacturers offer them.

Just from the Honeywell FocusPro 5000 & 6000 PDFs:

TH5320C1002 Up to 3H/2C
TH5320U1001 Up to 3H/2C
TH5220D1029 Up to 2H/2C
TH5220D1003 Up to 2H/2C

TH6320U1000 Up to 3H/2C
TH6220D1028 Up to 2H/2C
TH6220D1002 Up to 2H/2C

Jamie Hall

I've got to be missing something here.

To my -- admittedly simple -- mind, what we have is a steam heating systems with two boilers and, somewhere, a thermostat.

The two boilers are controlled by two vapourstats.

Now... the thermostat senses that the place is cold. Requests heat. The way I would set this up -- and remember, this is just me and I like things really simple! -- this would send power to both vapourstats which, being closed (boilers off) would fire both boilers. The system rapidly and happily comes up to some low pressure -- I forget what you are running -- and vapourstat A opens. Boiler A shuts off. One of three things happen: One, Boiler B can handle the load and fires constantly until the thermostat is happy. Two, boiler B is still a bit large, and fires until its vapourstat trips. System pressure drops. Boiler B's vapourstat -- which is set to cut in at a slightly higher pressure than Boiler A's -- cuts in and this repeats until the thermostat is happy. Boiler A never starts again on this thermostat cycle. The third option is that Boiler B isn't quite up to it, and the pressure drops until Boiler A's thermostat cuts back in, and boiler A fires until its vapourstat opens.

No relays. No fancy wiring.

What, folks and especially Colleen, am I missing?

If you want to get fancy, you could wire in a DPDT manual switch and trade the two vapourstats between boilers once a week... equalize the run time on each boiler, more or less.

Fred

I agree with you @Jamie Hall with two vstats,(that she already has), I see no reason to add a 2 stage thermostat into the mix. Besides that, she'd have to have some pressure control device on each boiler anyway, for safety sake.

hvacfreak2

The relay is there to isolate the two control power sources I'm sure.

But it brings up a good point , have a written sequence of operations posted at the machines . Imagine going to typical residential heat pump calls all week and then walking into a job with twinned sub atmospheric boilers that aren't staging as desired. Not that that is the case with the service guy on this but at some point it could be.

ratio

Are you kidding? I'd love to walk on to a job & find twinned sub atmospheric boilers! Instead, I'm moving the pins into the correct positions on factory wiring harness.

vaporvac

@ChrisJ , my Tstat (see my system description) is two-stage. MANY run at least that as they control zoning on HW systems, heat pumps, etc. Mine only has two stages. Jstar told me this is the control device I must have along with a Taco Relay.
Yes, I could get by with just the Vstats, but that means both boilers ALWAYS fire on start-up. With vacuum, and probably without, my lead boiler will raise the temp on its own after a set-back, so that's a big saving of Btus. After seeing how rarely my Vstats tripped I've concluded I need to hook up 5-wire to the Tstat and do it properly. I can see how one wouldn't need the two-stage Tstat on an oversized system, but mine is very closely matched. @nicholas bonham-carter , It is true, I probably don't need the one Vstat at all, but I didn't know that when designing everything! The "master" downfired my burners to exactly match my connected edr....I had planned on the upper burn rate. Also, when I just disconnected it, it shut off the boiler entirely.

hvacfreak2

ratio said:

Are you kidding? I'd love to walk on to a job & find twinned sub atmospheric boilers! Instead, I'm moving the pins into the correct positions on factory wiring harness.

I hear you , but you're an exception. The average guy banging out 8 in a service van is just looking for something that has failed , making the repair , on to the next one.

vaporvac

I cleaned the Vtats and the header piping, and checked connectivity to everything but the Taco relay. There are too many wires in there for me to know what to do and I'm afraid of screwing something up and ending up with no heat. The vstat header had some filthy water in in, but the pipes to the Vstats seemed clear. They sit about 1 foot above their little header so there's quite a bit of distance.

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.

BobC

Sounds like something in the relay area is at fault. Is it wired with stranded or solid core wire?

If it's solid core try pulling on the end of each wire, sometimes a break occurs under the insulation, if the wire begins to stretch that's the problem.

If it's stranded and they crimped spade lugs onto the wire make sure they stripped the wire before crimping on the spade lug. Ask me how long it took to find that one inside a control cabinet with over 100 wires!

Sounds like it's time to call in a tech if either of those scenarios doesn't pan out.

Bob

hvacfreak2

I agree with @Jamie Hall , it sounds like there is more wiring than there needs to be. I think his operating sequence is on point as well.

I'm sure that a wiring diagram could be drawn up in this thread , then it's just a matter of getting the wire in place. Have someone tag each wire on each end if you end up re wiring the controls.

Fred

Why not ask the gas utility to come out and check the pressure at the meter and at the boiler. They provide that service at no charge and it would eliminate that possible issue. If you call them out, have them check the pressure at the boiler with one boiler running and then with both running. Also, is there a pressure regulator anywhere near your gas meter or on the gas line? If so, those have a diaphram in them that could fail after a number of years. That's a gas company issue also, typically. I know you clocked the gas but, with the numbers you got, pressure is still suspect, in my mind.

nicholas bonham-carter

The purpose of the 2-stage thermostat is to see if the lead boiler, in mild weather can keep up with the heat demands, when operating subamospherically. Without that, both boilers will fire, as the pressure is below the vaporstat cutout.
In the shoulder season, the lead boiler may be able to hold its own, without firing the lag.
When a polar vortex comes along, the 2nd stage senses that the temperature is still dropping, and fires the lag.--NBC

vaporvac

Yes, @nicholas bonham-carter . That's the approximate theory! It also will only fire one boiler if the temp differential is small, such as it is now. I don't mean to suggest this is the only way to do it. It's just how Jstar and steamhead suggested, so that's what I did. The relay is just a central device and all the wiring from the Tstat, burners, spill switch and Ptrols and Vstat goes into it. It's not a fancy device. I think it's good even without a two-stage tstat.

I'm crossing my fingers, but we may have it fixed. Just running some tests now.

Jamie Hall

I quite understand where you are coming from, and why, with the somewhat more complex control system (and HVACFreak, you are probably right about the relay).

However, that said -- you absolutely have to have a complete wiring and logic diagram for the system, and an operating description. Otherwise it would be very difficult (as you have discovered!) for someone coming in who had not been involved in the design to figure out, in the presence of a problem, what it was supposed to do, and thus correct the problem. The more complex, or the more tightly engineered, the system is, the more necessary this is.

Having been involved in such projects -- though not in heating -- in a previous life, I can assure you that yes, a competent engineer can reverse engineer pretty nearly anything and go from there. But it's a lot simpler if someone has the original design!

Do not take this as a criticism in any way -- I've been very happily watching your progress with your system for quite some time, and I'm delighted with what you have achieved! I just want to be sure that you can keep it up to par!