Short Cycle new steam boiler . . Pressuretrol?

Daniel_3

Your pipes may be insulated with asbestos. How would you know unless you checked?

Calculations must be made to figure out your pressure settings. Yours has an additive pressuretrol while I have a subractive. To figure put the proper pressure settings you must measure the length of the longest main double it, adding all angle valves and elbows. We're working with small scale steam systems but if you had 200 feet of main with it's elbows and valves and have a 1 ounce pressure drop per 100 feet designed into the piping at the end then you'll need 4 ounces to get the steam to the last radiator take-off.

Since we're working with smaller pipe and less of it we don't need a lot of pressure but we can't use too low of a pressure or the steam will not be supplied properly to the amount of the connected load hence the lowest setting on pressuretrols is 1/2 psig cut-in. We need to overcome the pressure drop. I would like to find out whether this is related to my system piping and the pressuretrol settings. I'm not sure why the burner was short cycling at the end.

Daniel_3

I just noticed this today while relaxing at home(sick). After fire the burner cuts out then back on almost immediately near the end of the cycle right before the stat is satisfied. The Pressuretrol is set to 1psi main and .3 psi diff. approx. I may have been too conservative on the pressure and being that I don't have a vaporstat it may be too low for exact pressure control. This is a newer install just a few months ago. Drop header, full size near boiler piping on a IN 7, both supply's used, proper main vents, clean boiler water after more than sufficient skim taps and return/loop purging. EI package with probe LWC. LWC not experiencing low water. Level is fine just below halfway on the glass. Never experienced this before now on this coldest day of this season. I'm thinking this is related to the pressuretrol after more than a few firings this cold day coupled with last night's 0 degree ambient temps. Shall I keep the main to 1.5 and the cut-out to ride more than .3?

Daniel_3

I just set the diff to .5 and the main kept at 1 and it still entered into the same scenario. I had set the stat to 68 and before it was satisfied the burner cut off and back on again a few times.

Captain Who

I don't know, mine does the same thing if it's cold enough for the burner to run long enough to reach the cut-out point (I have mine set to cut out at 1.5 (really measures 1.70) and cut in at 0.5 -as low as it will go). I'm wondering if the fuel saved by not over-pressuring the system is more than made up for by having to re-fire the boiler after just a short down time. In other words, is there fuel wasted in the beginning of the firing which would tend to cancel out the fuel saved? I think I'll leave it alone for now.

I wish the pipes that are inaccessible inside the walls were insulated. Maybe this would help to hold pressure longer, especially when it's really cold outside.

Daniel_3

On top of what I already knew that may be affecting the short cycling is this: My connected load equals 474 edr making about 117000 btu's and my mains are 2". I've actually over reached the maximum edr (btu's) for that main size according to LAOSH. I need 2 1/2 mains to overcome the shortfall of about 96,000 btu's that the 2" supply's at maximum. Of course the radiators get hot and the house is comfortable but I'm a perfectionist.

Captain Who

I don't disagree with anything you said, but I wonder what really is the definition of "short cycling" when it comes to the pressuretrol settings. How long does the burner have to be off for it not to be considered short cycling? We're supposed to ride the wave on the pressuretrol settings, for the sake of fuel efficiency, that's my understanding anyway.

One thing that might be hurting me a little bit, is that the previous homeowner installed this boiler himself and he didn't pipe the equalizer and hartford loop completely right. He put the top of the Hartford only 1/2 in. below the NWL. Also, he didn't use a reducing elbow at the top of the equalizer. I have to keep the water line a little on the high side to compensate. Also, he has the header just a little undersized and only used one takeoff from the boiler (which is supposed to be OK, actually). Because of the high water line and the small header, I have less steam volume in the near boiler piping. The son of a gun used a lot of copper piping too, but that's another issue!

Daniel_3

Well the short cycling is the burner firing on/off at too frequent an interval. I would put too frequent being every few minutes. Mine is at the end of the cycle at every 5 seconds! Good thing this is not constant as I would have a short life span on the burner assembly and a huge fuel bill. My fuel consumption has dropped about 30 percent since the new boiler. That I enjoy immensely.

mel rowe

HO here with a thought that I'd like to throw into the mix. IF (1)your mains are adequately vented, (2) your system was balanced very, very well,so that all the rads get completely hot about the same time, and (3) the area around the thermostat warms up last, so that the stat stays on long enough, then why would the system build pressure enough to start cycling? You might think of it this way. What if all the rad vents snapped shut at the same time the thermostat shut off? I wouldn't think you'd see any cycling at all. In your case, if you are only seeing one or two cycles it sounds like your system is pretty close to optimum. Of course there are other considerations such as how well the boiler is matched to the load, but you don't have a lot of leeway on that. FWIW

Daniel_3

True that if the vents shut upon steam at the same time the thermostat is satisfied there may be no short cycle but even when the vents shut the rad still takes steam because a vacuum is produced by the steam turning to condensate and more steam is pulled in hence a radiator gets hotter and hotter. Short cycle could still occur because of the Pressuretrol not the tstat. Of course the most important matter is comfort without over-heating spending more money than needed.

I maintain 65 degrees normally while at home and 62 while sleeping and not at home. My home is comfortable. I am just curious about the short cycle whether it is normal or not. I haven't experienced it before so it's a strange beast to me. This super cold day has something to do with it. I believe the piping and the pressuretrol settings has something to do with it.

Captain Who

When I checked mine this morning it cycled off on the pressuretrol and I'd say it was off for only about 3 minutes tops, before it dropped to the cut-in and refired. That was when the house was trying to warm up from the overnight set back temperature on the digital thermostat. The rest of the day when I've checked it, the thermostat has stopped calling for heat before the cut-out was reached.

I haven't calculated the pressure drop in my mains, yet, but the system is working well. I have no main vents, just vents at the end of my dry returns. Don't know how I feel about this. There is no plugged tapping at the end of my mains where I could put main vents. I guess the vents at the end of the dry returns need to be sized only large enough for the steam to push the air all the way out of the mains quickly. In other words, I don't think I need to fill the dry returns with hot steam, necessarily, although this does happen when it's cold outside. Anyway, I have insulated the dry returns also, right up to the vents.

Still wondering if I'm short cycling. I agree that it will be more wear and tear on the gas valve, but what about efficiency?

Daniel_3

There's no need to charge the dry returns since they only function to drain condensate and not radiate. I installed main vents and saw a big difference versus the vents on the ends of the dry returns. Even if there is no plug just remove whatever short section of 2" pipe and install a tee 15" back from the end and at least 10" up. More height is best. That takes away the need of steam pressure to push out the excess air of long dry returns. It's more efficient. Also if the returns are insulated I have heard it increases carbonic acid build-up which grooves the returns moreso.

V8toilet

Stupid question but you didn't say that the pressure gauge was actually reading steam pressure at the pressuretrol limit. Is the steam pressure gauge registering at the high limit of the pressertrol when the boiler cuts out? I ask because it could be caused by the low water cutoff doing that.

Daniel_3

I almost never have seen the pressure gauge read anything higher than 1 psi if anything at all. I've seen it once or twice after a longer degree satisfying but then again I'm not always staring at it. This time the gauge picked up nothing. I have since tried main at 1.5 and diff at 1 to see what happens. How could the lwc be related if water level is normal? There's no abnormal bouncing.

Daniel_3

Let me add for those that aren't familiar that my connected load is 474 edr and the IN-7 gives 533 sqft of steam . The IN 6 covers only 450. This is the reason I went with the 7 section. I also intended to maybe add a radiator or two which would be a good choice given the age of the house and envelope.

Tom Hopkins

... what is short cycling?

Daniel, here is another data point. My house is 2 stories, 1900 ft2 with a 2 pipe vapor system.

Once Vaportat pressure is met for the first time, the boiler still cycles off and on frequently. At a 1 psi cutout and at least an 8 oz differential, it only takes 60 seconds for all the steam pressure to dissipate and then the boiler fires again and runs for another minute.

I did 2 experiments to better understand the problem. One of the radiators is large relative to all others in the house, with an EDR of 67.5 ft2. With the supply line to this radiator full on, the boiler would remain off for 40 seconds, then cycle on for 145 seconds. These cycles repeat consistently until reaching tstat cutoff. With the inlet line closed to this radiator, the cycle times changed to about 60 seconds off and 60 seconds on.

Then I tried to understand the rate of condensation or pressure loss. When the boiler shut off on pressure (and the large radiator off), I quickly unscrewed one of the main vents (with safety glasses and gloves!) and timed how long it took until the boiler cycled back on. It was 53 seconds relieving all the pressure through the main vent opening, compared to 60 seconds with the vent in place (and closed).

There is no audible or visual signs of steam loss in the system and the water level remains constant for an entire week with the auto-fill off. All traps are working correctly. Based upon input from the experts here (See Brad White's post on 1/01 on cycling and condensation), I'm thinking that the cycling is a function of the condensation rate in the convectors, radiators and pipes.

The lower the system pressure, the less time it will take to dissipate that pressure in the form of condensation. The more thermal mass you have in the form of iron and steel, I would think would equate to longer off times once all was hot.

Captain Who

I agree, this is what I was getting at when I said that I have fully insulated my dry returns (one pipe system). The faster that steam in the dry returns condenses (collapses), the quicker the residual pressure in the boiler will drop down to the cut-in point of the p-trol. I have brass dry returns so I'm not too concerned with carbonic acid. I think that could be taken care of with additives to control the pH anyway. Reducing heat loss in all the piping by insulating is important.

How much gas is actually wasted in the initial firing anyway? Does anybody know? If there were no gas wasted, the only downside to rapid cycles would be wear and tear on the gas valve, and flue damper.

Daniel_3

Definitely interesting and I did see the post from Brad. Funny thing is this never happened in the past three months since this boiler's "steaming" inception. I don't see how the cycling would change so suddenly given no change in the system. Maybe installation of some more radiation is due to further meet the boiler's steam output. I'll have to experiment more. It seems to most be related to the pressure in the system at the end of the cycle. The water in the boiler is hotter than normal due to insulation and more fire-ups. How could this translate to more volatile changes in pressure drop at the radiator vents and the set limit at the boiler to produce rapid on/off at the end of the cycle?

Tom Hopkins

your 5 second cycles

do not really make sense from a pressure standpoint. If the boiler were to fire for 5 seconds, I doubt that it could make enough pressure to cut out again. I know on my vaporstat, there is occasionally some bouncing in the switch just before it cuts out. I can not recall the innards of my pressuretrol, but I'm curious whether you could be getting an intermittent shutoff, especially with such a low differential.

The radiator vents are only venting air ... if the radiators are filled with steam when the pressurtrol kicks off, it's hard to believe that anything has changed there to make you super short cycle. The rate of condensation should be more or less consistent.

Does the problem go away if you increase the differential?

PS - I'm a homeowner with lots of troubleshooting experience, not a heating pro .... the experts opinions count more than mine every time!

Daniel_3

No, after the diff was increased the super short cycle did not go away. It does this maybe 5-15 times at the end of the cycle. Steam air vents vent air but they also breath. My Pressuretrol may be out of calibration, it's totally possible. This is standard equipment with the Burnham IN-7 so it's definitely not the cadillac of pressure control. The Old honeywell mercury switch on the Delco was very finnicky at low settings. The switch would get stuck and the boiler would not fire.

I don't see how condensate production has changed at all. The steam only knows it's load so the outside temperature shouldn't matter at all. The only change is the increased firings based on the dropping temps in the room with the thermostat. Right before this cold snap the firings were normal to my standard. It would fire, steam would fill, and the stat when satisfied would cut circuit. Pressure differential in the entire system has not changed from what I see. Somehow the burner is causing the burner to shut-off and on very quickly. This does not happen very consistently either. It will fire for 2 seconds then off then on, 6 seconds then off and on, then 2 seconds, then 10 seconds, etc. Very strange. The pressure gauge that comes with the Burnham is very cheap of course so I can't see what's going on for pressure readings.

I usually wake up early for work but I'm sick and won't be going today therefore I have time to post this much

Even if I splurge on a Vaporstat, will this cure this issue, I don't believe so. The L404 may be faulty. I never filled the pigtail and assume it's got enough condensate for the seal. About a month ago I brought temps up about 5 degrees and the gauge read a steady 1psi without burner turning off. Nothing changed. I'm definitely not seeing this pressure now as I did then.

Tom Hopkins

Root cause?

Daniel,
This chain has gotten long, so I apologize if I missed something you already said. If I were in your shoes, I would try to figure out exactly what is causing the cycling. What I mean is verify that the pressuretrol is actually cutting in and out at the end of the cycle. If it is , then focus on whether the pressure is not steady (is the water line bouncing up and down?).

Daniel_3

I just cleaned the pigtail and elbow. It did have some sludge. I refilled the syphon with clean water and re-installed. I will need some special equipment to check the actual pressurtrol cut-in and cut-out since I can't rely on the pressure gauge to read. This gauge is not reliable for this. The boiler fired just recently after the pigtail job and the short cycles are sort of erratic. There's no real consistency. Could be the thermostat calibration, could be the pressurtrol. I may have to call someone with the proper know how. In any case I can pretty much determine it's not a serious issue.

Captain Who

Just try this simple test (disclaimer: I have not actually tried this yet): Remove the pressure gauge from your tee after the pigtail (is this where it is? I can't remember) and screw in a hose barb that will fit some clear vinyl tubing. Blow the water out of the pigtail and into the boiler (just for this test). Attach one end of the tubing to your basement ceiling rafters. Leave this end open to the atmosphere. You are making a U-tube manometer. Fill the tube now with water so that you will have a U filled with water about 30 in. on each side. Attach the end of the tube to the hose barb and secure it tightly with a hose clamp so no leaks. Now when the boiler fires the difference in height of the two columns of water will indicate the steam pressure. You will now be able to accurately determine what the cut-in and cut-out pressures are and wether or not your pressuretrol is working properly. Don't forget to refill your pigtail with water before replacing the pressure gauge.

Another way to do this is the way Dale does it (Thanks, to him), which is to attach a hose barb to the drain fitting on the bottom of the boiler and attach the clear vinyl hose to this, with the other end attached to the ceiling and open to the atmosphere as above. Then when you open the drain valve, the water will fill the tube and be at the waterline of the boiler, with the boiler not firing and steam pressure zero. When there is steam pressure, the height of the water column above the previous zero level, will indicate the steam pressure accurately.


Please let us know what it is, and how it varies, I am curious. Also, I have attached the testing procedure for the vaporstat (you have the L408J?). I am between jobs at the moment!

effiweefewelp1875291

I have the L404F 367 pressuretrol. I had read through that manual but don't have an ohm meter. To my surprise I had been meaning to get extremely balanced main venting. I have two mains, 2" , 31 feet, and 36 feet. One had a gorton #1 and the longer had a gorton #1 and heat-timer varivalve. I just replaced the heat-timer vari-valve with another gorton #1 to make two as the shorter main would still beat out the longer with the vari-valve in the fully opened position. Guess what no more short cycle on a full cycle from 61 to 65 degrees. It doesn't make sense to me. I'll keep an eye on the cycles to see whether there is another frequent burner off/on before the tstat is satisfied. This is weird.

Captain Who

Hmm....so you're saying that the pressuretrol didn't even reach the cut-out point before the t-stat was satisfied with the new venting configuration?

effiweefewelp1875291

Yup. Strange. I also had put the diff to .75 and the main back to 1. I can't explain it.

joe lambert_2

Well I'm sure you know if you have read Dans books that what you see going on in the gauge glass isn't what's actually going on inside the boiler.

What you should do is verify what safety system is actually cutting off the burner. Is it the pressuretrol or the low water cutoff shutting off the boiler because it senses a low water condition. A simple test is the raise the pressuretrol setting TEMPORARILY way up to say 4 psi cut in and 6 psi cut out and watch that pressure gauge while it's steaming. If the boiler cuts out before the pressure reaches that setting than something is definitly wrong with the controls there.

joe lambert_2

settings

sorry

joe lambert_2

settings

Well I'm sure you know if you have read Dans books that what you see going on in the gauge glass isn't what's actually going on inside the boiler.

What you should do is verify what safety system is actually cutting off the burner. Is it the pressuretrol or the low water cutoff shutting off the boiler because it senses a low water condition. A simple test is the raise the pressuretrol setting TEMPORARILY way up to say 4 psi cut in and 6 psi cut out and watch that pressure gauge while it's steaming. If the boiler cuts out before the pressure reaches that setting than something is definitly wrong with the controls there.

Captain Who

Update ?

Is your system short cycling anymore, or is it - So far, So good? Improving a deficient main venting could definitely effect the pressure drop in the system, which might help to prevent the cut-out pressure from being reached, at least until the vents all close. But maybe in the extra time that takes, the tstat becomes satisfied and stops calling for heat. Thats all I can think of, as to why it might have fixed your problem.

effiweefewelp1875291

I agree with you on this one as there seems to be no other reason. No more short cycling also Capitan. Skipper out.

effiweefewelp1875291

I wasn't concerning with the gauge glass. I have already cleaned that once or twice and with each skim, and even a full dump of the system's water the gauge glass is equivalant to the true water line. Now way that the near boiler piping as I configured it according to spec and even more conservative in that respect would the column rise any higher and entrch the mains or back up into the returns. This is related possibly to the pressuretrol not being very accurate. The LWC does not relate to this situation since the water did not reach that level. I have tested it several times. What I haven't done is get a clear diagnostic test done for the pressurertol. I will try to set up a U-tube and check it in time though. With main vent swap the problem is solved though so I can pretty much say the short cycling is gone for good, for now that is.

I tried the main scale at 4 psi and it still cut out but this was before the vent change. I'll try and see if that will prove the pressuretrol is working accurately.