Steam two pipe pressure concerns?

JoshP

My two pipe steam system has been working hard lately. I'm in central ny and its been a heigh of zero the past four days. Now the boiler has been running for more and longer periods of time since its been so cold. My boiler started short cycling. Not all the time though. Seems most likely at night and in morning. Haven't had this problem before. when it does happen it will run for about 10 or 15 min and the pressure on the gauge builds up. then it trips and shuts down for about five minuets. Should I be concerned and have venting problems or is it common when the boiler runs for longer extended periods of time?

nicholas bonham-carter

Short-cycling

What pressure is it cutting out at?

Where does the air escape from the system?

Have your pressurtrol, and pigtail been checked/cleaned, lately?--NBC

JoshP

Short-cycling

What pressure is it cutting out at? - my gauge says about half a pound maybe. It's a very old gauge and I'm not sure if the scale is correct as the gauge goes up to 10 lbs. should I replace it ? Suggestions on type to replace with ? I will upload a pic later.



Where does the air escape from the system? - I have a main vent at the boiler off the return lines. Three smaller Groton vents.



Have your pressurtrol, and pigtail been checked/cleaned, lately?- pigtails for pressuretrol and gauge cleaned two years ago. How often should they be cleaned? Pressuretrol checked two years ago also. It's cranked down to pretty much as low as it will go on both settings.

nicholas bonham-carter

Testing the gauge

If you switch the boiler off, and remove the gauge, then you can check the opening for any buildup. You could try to blow through the pigtail as well to see if it is clear. The gauge should move a little when you blow into it. The most accurate way is to get a 0-3 psi gauge, and put it on as well.--NBC

JoshP

Gauge

Here is the gauge. Pressure will run up to about 1 or 1.5 pound then kicks boiler off. Note pic is side ways.



Would plugged pig tails cause the pressure to rise and shut the system down? Or do I still have other problems ?

DrDomm

Me too

See my thread...this is what mine is doing.  Upstate NY sucks.

[Deleted User]

Pressure

If you have the pressuretrol set as low as it will go on both settings, and you're getting up to 1.5 psi on the gauge, it seems likely it's cutting off on pressure, doesn't it?  I found if you remove the cover of the pressuretrol, there is a mercury switch in there and you can watch to see if it switches off as the boiler does (at least mine is like that).



BobC recommended two gauges earlier:

http://www.grainger.com/product/Press-Gauge-18C773?functionCode=P2IDP2PCP

or

[url=http://www.valworx.com/product/low-pressure-gauge-25-0-3-psi]http://www.valworx.com/product/low-pressure-gauge-25-0-3-psi



I ordered the Grainger one - about $45 with shipping.  The front transparent faceplate is cheap plastic and it doesn't stay on very well.  If you're into quality you might want to go with a valworx one.  Ideally you would add the second gauge and leave the 0-30 psi gauge as they say codes require it.



Disclaimer - I'm not a steam pro and not even a well-informed homeowner.

conversiontime

set therm flat with no swing on coldest days

On the coldest days of the year your boiler must run much longer than normal to get same therm rise. If the therm is running on any swing (e.g. 65 at night and 70 at 7AM) then you will see pressure build on the longer burn time unless your boiler is perfectly sized (rare).



So in my case when the temps drop below 0F I permanently override the boiler to a fixed non swing temp until the spell passes. The boiler runs more frequently this way but you will not see the pressure building on a long swing burn.

JoshP

Short cycle

I had a feeling it was due to this cold weather since it's been fine until this cold snap.

Your comment

"So in my case when the temps drop below 0F I permanently override the boiler to a fixed non swing temp until the spell passes. The boiler runs more frequently this way but you will not see the pressure building on a long swing burn."

Can you explain how you do this? Pro no pressure build up? Con runs longer so more $$?

conversiontime

short cycling is most ineffecient

sorry, the therm allows for a "perm" override that keeps at set fixed temp. This way I can then hit "schedule" button and it reverts back to normal schedule without re-program. I prefer to keep the house cool at night and while at work so generally 2xdaily it runs a 4 temp swing. During cold spells the boiler cannot hit this swing without building some pressure hence the override.



Every system varies but my boiler is pretty big and seems to work best on a 30-40 fire time relative to best efficiency. The swings are around that time frame, otherwise it averages about half that to keep static. Not sure if it matters though as they honeywell therm I use is "smart" in that it basically fudges therm readings to keep illusion of flat temp. But that is another thread!

JoshP

Short cycle

I actually keep my thermostat at 67 all the time. I can program it but "override" it all the time. I was under the impression steam doesn't like big swings in temp.

So back to the temp outside being the culprit? It's been around 0 to 5 or 10 below at night. I noticed the boiler kicking on about 45 min after it's last cycle last night. That is obviously not typical. Is the system not getting enough time to cool down?

Jamie Hall

Hey folks...

It's cold outside.  That's all there is to it.  The colder it is outside, the more heat the building loses.  Therefore, the more heat the boiler has to put into it.  So... the boiler will run longer or more often or both, depending on exactly what kind of thermostat you have and how it is set up.



If it is a question of longer, it may be that it is finally running long enough at a whack to reach the point where all the radiation is condensing steam as fast as it can, and the boiler -- being slightly oversize as most are, for good reason -- produces steam faster than that.  So... the pressure will rise and the boiler shuts off on pressure long enough for the radiation to catch up, when it comes back on.



Just doing what it's supposed to do.



The question concerning setbacks is an interesting one.  With some types of heating system -- notably forced air -- they make some sense; the room may be cooler (it will be close to the average of the two temperatures of the setback) but the warmer air may make people comfortable; interestingly, folks running setbacks like that usually run a slightly higher temperature than those who don't, since the warmth of the structure and furnishings compensates for the slightly cooler air.  On steam, though, they make much less sense, as the system responds much more slowly to the change: you have to heat the radiation first, then -- eventually -- the air.  Do setbacks save money on steam or radiant or hydronic systems?  Hard to say; the jury is not just out, but on vacation somewhere.



If you do run a setback, though, the system will, obviously, have to run a lot longer coming out of the setback than it would if you held a constant temperature.  Indeed, depending on the structure and the outside temperature and the power of the heating plant, at some point it will never make it and the boiler will just keep running and running...

ChicagoCooperator

Same problem I'm having..

Our boiler is running pretty much non-stop right now and stopping on pressure. However, it's not consistently restarting - the burner has to be reset a few times a day and, of course, not happening when the boiler guy stops by to check. And having mainly convectors means a quick cool down in places too.



(for those of you who followed my previous rant, my ally on the board and I are going to force the issue of bring in Dave B to evaluate the system and have expert advice to "force" the issue of "we need you to fix this/that in your unit" - most of our building is on the warm side while a few units are barely in the 60's..)

steamedchicago

setback efficency

Heat loss goes up with temperature differential.  So if you're 70F inside, you're losing more heat than if you're at 64F.   That's true whether is 63 or -63 outside.  



Let's assume those are your day and night temperatures. 

The heat you have put in to go from 64 to 70 is heat you would have lost if you'd kept the temperature at 70.  The savings from a setback is the difference in heat loss at the high temperature compared to the low temp, minus any excess heating from overshooting.  It doesn't matter if your system runs all day to reach the day setpoint five minutes before the setback kicks in again, or it if it makes it up in the first cycle.  If the outside temperature is above the design temperature of the heating system, and the set point is below the inside design temp (70F in most old steam systems), and the heat loss is no more than designed for, the system will eventually catch up.  That's because the heat loss below the set point is less than the heat loss at the set point, so there's spare capacity. 



A set back is only inefficient if there's substantial overshoot of temperature, or if there's large imbalance in the system (so someone opens their windows, because it's too hot, but also because the heat loss is higher at high temperature.).  If it's very cold, it can take a very long time to make up the heat loss, and it might be more comfortable to turn the setback off, but it won't be more efficent.  

Jamie Hall

So it would seem

but the thermodynamics of it are actually much more complicated -- much more than is usually appreciated.



The argument made is more valid if the comparison is between the heat loss at the mean indoor temperature (the weighted average of the upper and lower setback temperatures) rather than between the upper of the two setback temperatures.  Even there, it's complicated -- and indeed, no two buildings will react the same way, even if the proverbial "all else being equal" is achieved.



The debate will go on...