unit constantly cycling on low water, and consuming too much water

davidnyc

Short story - one pipe steam, 5 apartments. It's a coop, I'm the only techie cooperator and mind the boiler, but prefer to have pros do most of the work. Plumber who installed new boiler 6 years ago maintains it, owner is very smart and knows his stuff, and they are very responsive to solving go/no go emergencies, burst pipes, no heat, etc. I really like them. But in heating season they are running ragged (five or ten trucks, some very good techs, but they each have different ideas).

Radiators are hissing a lot more than they ever did, and boiler is cutting out on electronic low water cut off 3-5 times per cycle. System losing two gallons of water a day, or a full boiler worth twice a month. Water level is bouncing up and down no more than an inch. This problem seemed to arise after a 100ft return line was replaced. (Return line was undersized and not properly angled and pipes were banging like mad - new line totally solved that.)

To solve hissing and cycling, Plumber came and poured in a quart of 8-Way and unit ran through a number of cycles with almost no low water cutout. But the other LWCO - a six year old mechancial Mcdonell Miller 67 - crapped out completely 8 hours later shutting down boiler. In replacing that LWCO the boiler was drained, they did not dose new water with 8Way, and once again water is bouncing up to an inch, and the thing is cutting out on low water 3-5 times per cycle and consuming 2-4 gallons per day. (VXT-24 water feeder seemes to be working properly, boiler water level never goes too high.)

Years ago I had put a data loogger on the boiler, so here’s what the cycles look like. Day two long off time was separate heat timer issue, then that evening after 8way you can see smooth cycles, until it died, then off while they replaced LWCO.

davidnyc

Oh, I'm in lower Manhattan, NYC.

Abracadabra

davidnyc said:

..
Radiators are hissing a lot more than they ever did,

A sign of insufficient main venting and too high pressure. What's the main vent situation and what's the pressure the boiler is achieving during a cycle?

davidnyc said:

and boiler is cutting out on electronic low water cut off 3-5 times per cycle. System losing two gallons of water a day, or a full boiler worth twice a month. Water level is bouncing up and down no more than an inch. This problem seemed to arise after a 100ft return line was replaced. (Return line was undersized and not properly angled and pipes were banging like mad - new line totally solved that.)

Was the boiler skimmed after the new return line was installed? If not, then have them back to do that. Draining the water in the boiler is not skimming.

davidnyc said:

To solve hissing and cycling, Plumber came and poured in a quart of 8-Way and unit ran through a number of cycles with almost no low water cutout. But the other LWCO - a six year old mechancial Mcdonell Miller 67 - crapped out completely 8 hours later shutting down boiler. In replacing that LWCO the boiler was drained, they did not dose new water with 8Way, and once again water is bouncing up to an inch, and the thing is cutting out on low water 3-5 times per cycle and consuming 2-4 gallons per day. (VXT-24 water feeder seemes to be working properly, boiler water level never goes too high.)

If boiler is using 4 gallons per day you have a leak. Did anyone take a look at the guts of the old MM #67. With proper maintanance I've seen them last a couple of decades. I'm guessing the 8-way released a bunch of crap in the system which ended up in the float chamber of the LWCO.

KC_Jones

Sounds like the boiler needs a skim. Anytime piping work is done the boiler should be skimmed it's a fairly standard practice. The oils from the new pipe will cause surging and push water up into the pipes and can cause it to shut down on low water until the water returns. That does not however explain completely losing water (2-4 gallons per day). That generally indicates some kind of leak either water or steam leak. Have you checked all the piping? Any buried return pipes? That is very bad you should probably only consume that much water per year not per day. There is a leak and it needs located. You posted where you are, are you looking for recommendations to a good steam contractor?

Fred

His water bounce isn't bad and doesn't really suggest that skimming is the fix here. I suspect a couple things going on. His Pressuretrol may be set to high (.05 Cut-in and a differential of 1 is best) or the pigtail the Pressuretrol is mounted on is plugged with gunk and needs to be cleaned out.
Having said that, the more serious problem is the water loss. Losing that much water a day could well trigger the LWCO and you need to find out where that water is going. Hopefully when they replaced your return lines they didn't run a dump to a floor drain or something equally wierd. There is a leak somewhere and it may be in the boiler block itself.
One other thing to do is take the probe for the LWCO out and clean it well with steel wool and don't use any teflon tape when re-installing it. Those probes need to ground themselves against the boiler block.

davidnyc

Abracadabra - the main vent is a Gorton D, probably insufficient. The pressure was 3 lbs. the other day (when it ran long enough).

Is it possible the water is being lost through all the hissing steam valves? There are no buried pipes, and we have no indication of a leak, no steam anywhere.

KC- Yes, I'm looking for a good steam contractor in the city.

KC_Jones

A Gorton D is a radiator vent not a main vent. That is for sure an issue. The pressure is definitely on the high side should be about half that at most. If ALL the steam valves are hissing it could be, but that is a lot of water loss through steam. I hate to throw this out, but did you look at the chimney for steam coming out of there?

Abracadabra

davidnyc said:

Abracadabra - the main vent is a Gorton D, probably insufficient. The pressure was 3 lbs. the other day (when it ran long enough).

Is it possible the water is being lost through all the hissing steam valves? There are no buried pipes, and we have no indication of a leak, no steam anywhere.

KC- Yes, I'm looking for a good steam contractor in the city.

1 - fix your main venting.
2 - lower the pressure to 1-1.5
3 - 4 gallons of water is over 6000 gallons of steam. You'd notice 6000 gallons of steam. Is the boiler leaking water internally and it's going up the chimney? Pics of boiler please?

davidnyc

The return line replacement was a very nice job, nothing untoward there (except they used copper, which some of you frown on - I think I need to understand water treatment after solving immediate issues).

And I don't really "get" the whole turn down the pressuretrol thing. I imagine that you would reduce the pressure by turning down the flame - wouldn't turning down the pressuretrol just mean the boiler cuts on and off a number times on pressure during each cycle? Is thats okay?

Abracadabra

The analogy that's often used is that the empire state building uses 2PSI to heat the place. You don't need 3. It's inefficient, and beyond that.. also causes the water level in your boiler to drop more than it needs to. You can reduce the "pressure" by lowering the flame, but you don't have a modulating or 2-stage valve. Yours is either on or off. (I think, since I didn't see a pic of your boiler). The pressuretrol will cycle the boiler so that system pressure doesn't go over a certain level.

Fred

Steam moves faster at low pressure. The Pressuretrol is really a safety device but, when a boiler is maybe over-sized, it also acts like an operating control to keep pressure down. Once the radiators are condensing steam as quickly as they can, adding pressure to that is just a waste of fuel as the max condensing rate of the rads isn't going to change. So what you want to do is set the pressuretrol so that it shuts down when the system is full of steam. 1 to 1.5PSI is a good indicator that the system is full.
Under normal circumstances, the Pressuretrol is rarely called upon to shut the burner down because of pressure. The reasons for it doing so are:
1. boiler is oversized and producing more steam than the system can process
2. The boiler is trying to recover from a deep setback and running an extended period of time
3. The outside temps are extremely cold (near or at 0) causing the boiler to run for extended period.
4. The main venting is inadequate ccausing pressure to build as it tries to push air out of the way.

davidnyc

Thanks all. jStar is coming out on Monday.

Fred

Great! You've got one of the best!

Jamie Hall

"And I don't really "get" the whole turn down the pressuretrol thing. I imagine that you would reduce the pressure by turning down the flame - wouldn't turning down the pressuretrol just mean the boiler cuts on and off a number times on pressure during each cycle? Is thats okay? "

Cheer up. A very common misconception. The pressuretrol does not control the pressure at which the system operates. It simply controls the maximum pressure which the boiler can create -- and has been said, if therefore a safety control.

The pressure the system will operate at is controlled by the rate at which steam is being generated and the rate at which air can be vented out of the system -- they must balance. Once the radiators are full of steam and thus condensing steam as fast as they can, then you want to match the rate of steam production to the rate of steam condensing, They must match. The easiest way to do this is to sense the slight pressure rise when the radiators are full, and then turn the boiler off until some steam has condensed. Then if more heat is needed, turn the boiler back on to make a little more steam -- and so on until the thermostat is satisfied.

Note: "slight pressure rise". There is no point in making more pressure -- that's just burning fuel to no purpose. So set the pressuretrol to sense that slight pressure rise. 1.5 psi is ample for almost any residential systems -- and in some, such as the one I care for, even half a psi is too much.

As to the pressuretrol cutting off the boiler a number of times in a thermostat cycle... well, if it happens when maintaining a steady interior temperature, your boiler is oversized. "Turning down the flame" (technically, down firing the boiler) may help, but must be done by someone really skilled in setting and adjusting the burner. If it happens on a very long run, such as recovering from a setback, that's pretty normal. If it happens during a normal run and rather early in the cycle, that suggests that the main venting is inadequate.

SWEI

Jamie Hall said:

The pressure the system will operate at is controlled by the rate at which steam is being generated and the rate at which air can be vented out of the system -- they must balance. Once the radiators are full of steam and thus condensing steam as fast as they can, then you want to match the rate of steam production to the rate of steam condensing, They must match.

You just made the case for a two-stage gas valve on every steam boiler.

Fred

You just made the case for a two-stage gas valve on every steam boiler.
@SWEI , How do you stage a gas valve when pressures run at 1 to 2 OZ.?

SWEI

It gets tougher with well-tuned vapor/vacuum systems. You have to sense a few things and then learn the system. Time to preheat should be fairly consistent with perhaps a bit of weather influence towards the ends of the curve. @MarkS has a really good start on that with his EcoSteam.

Fred

SWEI said:

It gets tougher with well-tuned vapor/vacuum systems. You have to sense a few things and then learn the system. Time to preheat should be fairly consistent with perhaps a bit of weather influence towards the ends of the curve. @MarkS has a really good start on that with his EcoSteam.

I wondered about thermo sensors at the end of my longest main. That is pretty darn consistent.

Jamie Hall

SWEI said:

Jamie Hall said:

The pressure the system will operate at is controlled by the rate at which steam is being generated and the rate at which air can be vented out of the system -- they must balance. Once the radiators are full of steam and thus condensing steam as fast as they can, then you want to match the rate of steam production to the rate of steam condensing, They must match.

You just made the case for a two-stage gas valve on every steam boiler.

So true. I couldn't agree more. Unfortunately, I don't have access to natural gas... and LP around here is no better than oil. Someday... a fully throttlable (say 6 to 1 range) oil burner with a sensitive pressure control... ah yes. Dream on! Oh yeah -- and it has to be fail operational, and run reliably off a generator.

KC_Jones

@ChrisJ suggested this to me the other day to control my low fire since I am not building enough pressure ATM to trigger the vaporstat. That would probably do it, but cost prohibitive. Unless I can sell my vaprostat for a good price!?
http://www.dwyer-inst.com/Product/Pressure/DifferentialPressure/Gage-Switches-Dial/SeriesA3000

SWEI

Photohelics do kind of make for the ultimate Vaporstat replacement. Can't argue with the looks, either.

KC_Jones

I am not doing it. Honestly I fully expect a dramatic change once I get my insulation installed. I am waiting for that before I make any decisions going forward. If it doesn't change enough to justify the 2 stage valve I already have then I may just remove it or figure out a simple inexpensive way to activate it. Time will tell.

Fred

I agree that there is a point of deminishing return and also agree that, on a new boiler install, where the boiler has been properly sized, staging the burner probably yields little or nor return, other than maybe allowing you to mimic how the coal fired boilers use to run (on days when you built a smaller fire just to "take the chill out of the air" (as they use to say). But even that probably has to be timed in some fashion or an operator selectable (adhoc) option because changing outside temps demand different operational attributes.
I also don't necessarily believe that a down-fired boiler that runs for longer periods save any fuel (money) over one that is fully fired for shorter periods (may be more even/comfortable but even that is subjective to each individual)
For those of us that have over-sized boilers, staging on the 5 days a year when outside temps are 0 or below and the boiler is short cycling may satisfy our angst to stop the short cycling but I am torn as to weather the minimal benefit of reducing those short cycles justifies the cost. My boiler runs at 1 to 2 OZ. max, except on those sub zero days when I get enough pressure to trigger staging.
For anyone who short cycles on a normal heating cycle because their boiler is way over-sized, staging is a no-brainer.