Lead Boiler shut-down: cause?

vaporvac

I'm going nuts trying to trouble shoot an entirely new occurrence with my twinned boilers. Since starting them this season, they're working completely zonky. Normally both fire until temp is met or lag goes off on pressure. I've only ever observed it go off on pressure once prior as my system is well-matched to its EDR. After temp is met, I'll manually shut off the lag boiler (because I don't have the two-stage Tstat hooked up yet).

I have a big system with slowish returns. I've noticed the lead boiler going off on LW a couple of times last year when coming back from a set-back, but it comes on quickly.
Fast forward to friday's boiler servicing:
The technician said my boilers were running great, cycling on and off on pressure. I thought that strange since my system is well-matched and hardly ever reaches cut-out, but I was coming back from a cold start. He left and I kept hearing one boiler going on and off, continually. It was taking forever to get steam to the rads. When I checked only the lag boiler was firing. I shut it off, waited for a bit and turned them both back on..... same thing happened.
I though maybe it was a LW situation as it worked after the wait.
Today, I was sure I had clogged returns to the lead boiler, but when I only had IT on (manually shutting off the lag) It never shut down (except once at the beginning of the cold start on LW). Plus, the low Water shut-down level was LOW whereas the shut-down level yesterday was NORMALl water level height. So NOW I'm thinking it's not shutting down due to slow returns and a LW situation.

I also thought it might be the Vsat setting. I haven't checked out that theory yet, but if that's the case, why didn't it shut down on pressure during today's test with only the lead boiler firing?

Fortunately my house will heat with the lead boiler alone; it just takes longer. Unfortunately, when I have them both on the lead is the one going off constantly, so the house took forever to warm up.
What could be going on here? I'm flummoxed. I keep asking myself what is different this year? Did I change anything? No, just the service call to check the burners and clean them and the shut-out issue from a prior post.Thanks for any help. I need it.
Note: the tech found the vent shut in my lead boiler's burner resulting in bad co/02 numbers , but he fixed it and got great numbers afterward. We don't know how that happened as it's inside the case. Still, I can't think how this might affect anything with the on/off lead which only ever happens if both boilers are on.

ratio

Can you use a multimeter? I'd start looking for whichever control is shutting down the burner - that'd give you a better start on diagnosis.

I don't know if your controls are line voltage or low voltage, but a multimeter set to a 200 volt AC scale should read either safely. Put the black probe on a piece of bare metal somewhere (everything should be grounded, an alligator clip helps here), then put the red probe on the terminal for the incoming & outgoing wires. If the control is normal you'll read the same voltage on either side of it, if it's open you'll read ~ zero on the leaving side. If you don't know which is the leaving side you'll have to do a little more checking to prove which is the open one.

nicholas bonham-carter

It would be so convenient, if the control manufacturers would include a little tell-tale led light to aid in diagnosis of problems such as yours.
Alternatively, a terminal block with lights might serve the same purpose of showing where the electricity stops.
Maybe someone here can help with giving details for something like this.--NBC

hvacfreak2

Just a thought , you mentioned that he fixed a closed vent , was that on the lag unit ? I'm just thinking that he improved the performance of the Lag unit that is now much more " capable " than it was. Or even if it is the Lead unit that was fixed system pressure is coming up alot faster than it was. And then this thought , is that how the installer ( or the tech who set up the system ) got it to perform as required ? I do not know all of the specifics or history so this all may sound ridiculous . I have set up systems ( hvac ) that I needed to reduce the performance of something in order to make the system work .

vaporvac

vaporvac said:

I also thought it might be the Vsat setting. I haven't checked out that theory yet, but if that's the case, why didn't it shut down on pressure during today's test with only the lead boiler firing?

Duh! With only one burner running it would be hard pressed to reach pressure as it now "undersized".
@hvacfreak , to clarify, it was the Lead boiler's burner that was fixed. It worked very well prior with very good Eff numbers, just not 86%+.
Thanks for the insight. I figure it must be one or the other, ie. pressure or LW. It HAS shut off on LW, but the level was LOW when it did that. It's currently shutting off at a normal water level. that's why I don't think it's that. But, you're correct, a multi-meter will show for sure.
I'll fool around with the Vstat when I get home....I'm now wondering if he set them up backwards last year so when I adjusted the new one upward (which I figured would give the lead more "on" time), it was actually giving the lag more time on. I followed the wires to the Taco Relay, but I can't make out what it means. I'll have to really study the I&O manual. That's why I had someone else wire them in last year.

I just wonder why suddenly this year ?

P.S. I insisted on the same tech as he was familiar with my system and loves steam. He'd never actually seen a gas conversion burner, and wondered why they aren't more common.

ratio

It's a good idea to keep the same tech if you like him - at the very least, asking for him by name sends a clear message to the boss. With all the problems associated with finding good steam techs, any positive experiences should be noted. (n.b. I am a good tech, and am in favor of good techs getting good recognition--and good remuneration!)

ChrisJ

Do you have a decent pressure gauge on each boiler?
How's the water level? Bouncing more than usual or normal?

vaporvac

Wow! Thanks guys.
@ChrisJ , the water level is normal, no real bounce. I just gave it a good skimming and cleaning with the wand prior to servicing. I have the factory gauges on each boiler with their p-stats, and the single vacuum gauge on the header with the two V-stats. They all register pressure and go into a vacuum when the system cycles off. The vacuum gauge has smaller calibrations that the factory ones (it's my original), but it is NOT a 1-3lb. gauge. I have noticed that in repose, none of the gauges ever really returns to zero anymore, but always read a light vacuum even after hours on "off"

@Hatterasguy , i do take it a bit personally! It certainly keeps me humble. Time will tell if they're broken, though. Oh, and the on/off cycle is short (although I did have one actual LWCO when the H2O level was truly low. That was after firing for a while.), so it seems to be a pressure issue.
@hvacfreak , that is a very good thought, as well. I don't know how long the burner was "bad". Obviously not originally, but maybe for a while. I only had the Vstats hooked up late last spring, after which everything worked great. I guess the burner doesn't lock-up on a low air situation? If it is just now working properly I could see how it would build more pressure. I also think that my piping leaks self-healing also increased pressure in the system.
@ratio , thanks for the specifics on the multi-meter set-up.'ll try that this week if changing the Vstat setting doesn't help.
And going totally OT on my own topic, I so totally agree about the tech. He originally came to put in a new compressor in my old Victory fridge, but talking to him it was clear he loves steam, so he took a look at my system and was able to do the V-stat hook-up.

Fred

@vaporvac have you taken the probe(s) out of the LWCO and cleaned them well, lately? Also, are you sure your Main vents are opening? I remember last year when you forgot to turn the water feed off. It is possible some of those vents are plugged up and stuck closed since they sat unused over the summer.

vaporvac

@fred, I asked the tech if we should do that (clean the probes), but he said he checked their functioning so it wasn't necessary. If the Vstat change doesn't do it, I'll read up on it. I think I should be able to do that myself. Do you clean yours every year?

About the vents, I think it's working because I hear it expelling air, but I haven't physically gotten on a ladder to check it out. On the Trane VaporVacuum system there's just one vent on top of a choo-choo train looking contraption called the "Trane Air-eliminator". It was designed to eliminate air in large systems, but just has a single vent on the top. There are no markings on the vent, and I've never seen how to get it off, so I just leave it. I've never posted on the issue so I don't really know if I can change it. Great minds do think alike, however, as I had initially wondered if it could have gotten rusty due to that overfill last year.

Fred

@vaporvac , I have the old MM #67 float type LWCO so I don't have a probe. I do blow it down, once a week to keep the float from getting stuck or crud from building up in the float chamber. Also, I think you said your VStat was mounted on your Header. You might want to check that too just to make sure the opening on the bottom or the fitting it is mounted on isn't plugged and causing the Vstat to hold pressure.

BobC

One of the great things about the old mercury vstats is you could tell if they were tripped just by looking.

You really should find someone who can show you how to use a voltmeter.

Bob

vaporvac

@BobC, I'm on it this week. Just waiting on a friend's availability. I know I could Youtube it, but I feel better with a hands-on demonstration with anything electrical.

I do feel this is a vstat issue, as another member said the modern vstats click when tripped and I definitely heard a click at least once when near the boilers. If that's the case, it would verify my suspicion that the Vstat are wired opposite of what I asked. Hopefully, the lead /lag part is hooked up correctly. (I'm currently toggling on pressure, not temp.). However, if it is the Vstats, the question is why is it suddenly tripping now and not last year after they were connected? Oh well. One thing at a time

It's in the 70s today, that's why I'm not messing with the settings yet. I'll update if I have questions there. Thanks all.

vaporvac

I'm waiting till Monday to check out the connectivity with the multimeter. Meanwhile, I was able to adjust the Vstats. I put the lead to 16oz/2oz and the lag to 120z/20z. It had absolutely NO effect. The lead cut out before reaching 8 ozs, cycling on and off at very short intervals. The lag boiler stays on always. The water line didn't affect it either as it happened when the water initially gets pulled up at a cold start and when the level drops somewhat. It doesn't surge and once it drops, it's steady.

I experimented by shutting off the lag boiler and then everything is fine... the lead continues to fire normally, obviously not building much pressure as it's now under-fired.
I know I can't know anything for certain until I have help on Monday, but this is driving me nuts! I don't want to call back the service tech without some idea of the problem. I now wonder if it's somehow tied to that burner vent closing, but if that's the case why would it function correctly on its own. URRGH!

Fred

Is there any possibility that there is an issue with the incoming gas supply/pressure ?

vaporvac

Anything is a possibility, but why would it only affect the lead boiler and only when the lag is on as well. Do you mean some issue with the burner's regulator? How would I test for that?

Fred

Actually I mean has the gas company done something to reduce the gas flow or pressure into the house so as to be sufficient to supply one boiler but not both at the same time? Does a single gas line feed both boilers from the meter and then Tee to each boiler? Is the lag boiler the first boiler fed off of that line so as to cause the lead boiler to starve for gas when both are running?

vaporvac

Got it! They haven't done anything that I know of. The line feeds the lead boiler first, then the lag, if that helps. I am now wondering if it's something to do with the burner, but then why does it work when it's the sole one running?

Fred

vaporvac said:

Got it! They haven't done anything that I know of. The line feeds the lead boiler first, then the lag, if that helps. I am now wondering if it's something to do with the burner, but then why does it work when it's the sole one running?

I think we might be getting closer to the problem. It has to have something to do with the supply of fuel. I mean if the boiler runs fine when it runs by itself but continues to shut down when both boilers are running, I would think the gas pressure may be insufficient to maintain both boilers. I suppose it could be the gas regulator in one or the other boilers but I'm thinking it has to be fuel/supply related.

BobC

Try clocking the gas meter with only the lead boiler firing. This chart only goes up to 180k but you can easily deduce higher rates if necessary.

http://www.aprsupply.com/support/technical-support/checking-firing-rate-(clocking-meter)

I had to have my gas line replaced last fall when I found the gas pressure dipping under 5 in wc when the boiler was firing.

ratio

When the boiler shuts down, does the ignition board restart it's purge cycle/start sparking, or is it off off? If the gas pressure dropped low enough to lose the flame proveage, it should try to either relight or recycle. There may be an LED on the ignition board that may flash an error as well.

Jamie Hall

I may have missed it up there somewhere, Colleen, but have you really checked that both those vapourstats are calibrated correctly, and the same? It would be worth double checking, even if that doesn't turn out to be the problem. I really like your system and the way you have it set up -- but it wouldn't take much of an out of calibration error on one of the two vapourstats to mess it up.

Also, I forget. Do both of them come off the same connection to the header? And is there a snubber on that connection? They should, and there should be. Otherwise odd conditions in the header could mess things up between them.

nicholas bonham-carter

Test them by putting a jumper on each to prevent either one from cutting off the flame.
Also jumper out the thermostat contacts at the boilers to simulate a call for heat, and see what happens.
Radio shack have these jumper wires with alligator clips on each end.--NBC

vaporvac

Thank you all for the great suggestions. I will be doing all these tests tomorrow.... clocking gas (many thanks for the link), testing for continuity, switching Vstats and cleaning out the pipe the Vstats are on.
How do I clean the Vstat itself, in case some rust go in there when over-filled last year?

@ratio , when it shuts down all lights on the probe are off. I only have a Taco relay and those lights are always red and have been since day one. They never go green. I'm not sure if that because it's not hooked up to the staging Tstat. It stages on pressure now, not temp. There's nothing that can say ERR. I'm just going by the probe lights which indicate which boiler is running.
@Jamie Hall , both Vstats and the vacuum gauge come off one line that comes off the header. I have read your references to a snubber, but need to look that up as I'm fairly certain I don't have one.... just a 90 attached the header. I also need to read how to calibrate the Vstats. @MarkS calibrated the Honeywell 0-160z. before he sent it to me and the old White -Rodgers one seemed to be working last year. However, I did determine that the Vstats are wired to the boilers that sit beneath them, so that eliminated one possibility.
It's all nutty! , but we'll get to the bottom of it.

Fred

How do I clean the Vstat itself, in case some rust go in there when over-filled last year?
I doubt that it did. There should have been a little air in the tube that kept water/dirt from getting to the Vstats but while you have them off, just look inside the fitting that screws onto the header pipe/tube and make sure the little pin hole isn't clogged.
I really don't think it's the Vstats. If it were, the boiler it is attached to would ack flaky regardless of the other boiler being on or not. Seems like the same would hold true for the burner(s). That's why I think it likely has something to do with fuel pressure/supply.

vaporvac

It does seem coincidental that the lead burner had an issue and now it's flaky. I just though perhpas with only one boiler running the pressure couldn't build at all, but I do feel the problem rests elsewhere. I hope it's just the fuel pressure/supply.

ratio

According to the manual I found, if the burner is locking out, you'd have to push the reset button to bring it back on, so I think we can eliminate burner & fuel issues.

It still sounds like a controls issue to me. Any chance of getting a schematic or ladder diagram of the controls? Do you know the model number of the Taco relay?

Fred

If I understan Vaporvac's comments, the burner does not go into Lockout. This is in the Trouble shooting section of that manual:
4) The burner continues to repeat the starting cycle without going into lockout.
This is a very specific situation caused when gas pressure in the gas main lines is very close to the
value at which the gas pressure switch has been set. This can be corrected by resetting the gas
pressure switch to a lower level. The gas pressure switch, if required, may be supplied, or may have to
be field installed.

vaporvac

This is exactly what's happening, @Fred . On/Off, On/Off, but not locking out. It only did that once and the service tech said it might have been because of a call for heat without gas or the closed vent. I don't know which it could have been, if either, but it hasn't locked out since. TACO 2-stage switching relay SR501-HC. Here's a pdf with wiring schematic: http://www.taco-hvac.com/images/100-88.pdf

Fred

I know you have a tech coming (Maybe tomorrow??). If it were me, I'd have him start by checking the pressure in the gas supply line with the pressure setting of the gas pressure switch when both boilers are running and when only one is running. My guess is you have a pressure drop when both boilers are running. He should be able to adjust the pressure switch down some (there is a minimum required for the burner size) or maybe the gas company can put a regulator on the gas line to maintain pressure.

nicholas bonham-carter

Try the jumping out of the vaporstats, and the thermostat first to see if both boilers can run for a while, and if so, that would point the finger of blame at the vaporstat, or the 2-stage thermostat. Don't mess with its calibration, until you know it is wrong.
if that does not run the boilers, then look at the other safeties on each.--NBC

Fred

@nicholas bonham-carter right now she says she doesn't have a 2 stage thermostat. She is staging the boilers manually. Of course there is nothing wrong with testing the Vstats but since they each operate a boiler individually with no problem, I can't imagine that running both boilers together would have the affect that she sees on her lead boiler. IMHO

vaporvac

Hi everyone. I'll be attending to this in a bit after work. I actually have a friend coming over to show me how to test everything, not the tech. I didn't want him coming back until I have a better idea of the issue. If only he had stayed a few more minutes the first time to see if all was well, we probably wouldn't even have this post, as the issue was immediately apparent to me.
I think I'll disconnect the lead Vstat, just to see if that does anything. If not, I'll check the connectivity to everything, clock the gas and see where that gets me.

I'll still clean out my wet returns and maybe fix the piping that I never got back to to provide a clean-out at some point in the near future. The water return seems slower this year, but that's not causing any issues.
Hang in there folks: I may post a blow-by-blow on this one as I eliminate culprits. It's a cliff-hanger.
Thank goodness it's just mildly breezy and the house is still warm.

ChrisJ

If I was you, I'd buy a decent multimeter as I'm sure you'll constantly find uses for it.

Here's the cheapest one I'd recommend.
http://www.amazon.com/Fluke-101-Multimeter-Equipment-Industrial/dp/B00JT5RUUU

Though these are what I usually buy for people where I work.

http://www.amazon.com/Fluke-115-Compact-True-RMS-Multimeter/dp/B000OCFFMW/ref=pd_sim_469_4?ie=UTF8&dpID=41-Dj5G1sCL&dpSrc=sims&preST=_AC_UL160_SR128,160_&refRID=06TWDFJ7NV811KVTX85M


Personally, I use a Fluke 179 at home.

http://www.amazon.com/Fluke-ESFP-True-Multimeter-Backlight/dp/B00012Z0V6/ref=sr_1_1?s=hi&ie=UTF8&qid=1447096276&sr=1-1&keywords=Fluke+179


Even the cheap one will last you many many years and would make troubleshooting something like this a piece of cake.

vaporvac

@ChrisJ , we're using a fluke 16. so far we have power to both Vstats AND IT READS THE SAME FOR BOTH whether "on or "off". @Hatterasguy , why is it better to jump between the two terminals rather than just disconnecting it?

BobC

A vaporstat is usually used to shut a system down if pressure exceeds it's setpoint so using a jumper across the terminals will keep the system running. If the system runs fine with the jumper it means it's tripping out (pressure is too high OR the switch is flaky).

Bob

vaporvac

Thanks for the explanation @BobC . I jumped both boilers while running and they continued running.
Hmmmm.

However, I noticed something else happening. When the lead boiler shuts off, its corresponding red light on the Taco relay goes off, too, However, both lights should always be on when there's a call for heat, even if one boiler is completely shut off at the switch.The lag boiler works as designed ie. its red light stays on when I manually shut off the boiler. the only other time I noticed no red lights with a call for heat was last week when both burner locked out. Neither light was lit.
(Btw, the boilers will shut off as designed when the temp is reached on the Tstat.)

so do I have two problems, or should I do further testing with the Vstats?
I'm going to try clocking the meter now.

vaporvac

Do I need to adjust the inlet gas pressure as stated in the above link? If so where and how?

BobC

If you have verified that jumping the vaporstat keeps the boiler running I don't think the gas supply is a problem.

Go over all the wing to see if anything is loose. Do you have a diagram for how the vaporstats and relay panel are hooked up?

Bob

ratio

How were you checking the vaporstats? You'd need to disconnect one wire to check with the continuity or ohms (resistance) setting, or use the a.c. volt setting to check with power applied. With pressure below the cut in setpoint you should see either continuity or zeroish volts across the contacts as they should be closed. With pressure above the cut out setpoint you should see either no continuity or 24 or 120 volts depending on the control voltage.

You should also be able to hear the contacts throw if it isn't too noisy, & I believe you can see the position of the armature under the clear plastic cover too.

Mind the differential when you're expecting the contacts to throw.

vaporvac

Well I may have two problems then, because I clocked the gas meter and the lead boiler orifice is 240btu,but the meter is running at194Kbtu. The lag should be 200Kbtu, but it's running at 210btu. Together is SHOULD be 440Kbtu, but it's about 328K btu!!! What is going on here? The lead boiler is getting fewer btus than the lag and together it's way less than it should be. I clocked a few times and took the average and used another chart that gave the numbers I needed.
Also, my gas meter 1/2cft dial pulses and when both boilers ran together it had an audible knock. Is this normal?
@BobC , all the wiring is good.
@ratio, we just checked the voltage which was the same on or off. I didn't trip the Vstats. should I have done?