short cycling boiler

ljh_2

the glass is very quiet, not much movement, no more surging. the water looks pretty clean too. He put some kind of chemical in it (very pale green) after skimming it. seems to have done the trick.

ljh_2

boiler short cycling?

I had my old boiler (one pipe steam) replaced last summer with a Peerless 63 natural gas steam boiler by a professional listed on this site. He came back once to clean the boiler (had surging water, spitting air vents, and it was using way too much water)that's all working fine now. However, I think the boiler is short cycling (I have Dan's book - "We got steam heat" and have read it twice-sometimes a little knowledge is a dangerous thing) but I want to make sure I know what I am talking about before I call him back. When the boiler comes on - the steam pressure rises to 2 - 2.5 psi in 3-4 minutes, then shuts off, the pressure drops to .5 psi in about 1 minute, then boiler comes back on and the cycle repeats till the t-stat is satisfied. Is this the way it is supposed to work or is this short cycling?
I've read the hints on short-cycle and I'm not sure what to think. The pressuretrol and pigtail are new - so would they be clogged already?(the pigtail is facing correct way) New thermostat as well, and the air vents were all checked and non-working ones replaced already. I am assuming the boiler is correctly sized as the contractor took very exacting measurements of all the radiators before he gave me a proposal.
If this is short cycling, would that explain my December fuel bill? The pipes are all insulated (same as last year)I replaced the boiler hoping to gain some efficiency (the old one was 30+ yrs old and leaking) and I also had the house insulated and now have a set-back thermostat (last year no insulation and the house was at 70 constantly) and I am seeing no reduction in my fuel use (Dec '04 - 1095 degree days used 276 therms, Dec '05 - 1164 degree days used 257 therms - can't really compare $$ cause fuel cost is going up) Sorry for the long post - just wanted to give all the details.
Thanks

thfurnitureguy_4

food for thought. Was the radiation down sized when the house was re insulated? if you lowered the heat loss in the building and sized the boiler to the existing radiation. Wouldn't it now be over radiated for the heat loss? I would think that it would cycle on stat and not pressure if this was the case. So run the calcs add up the EDR on your rads and check the net I=B=R rating of your new boiler and see if they match.

Bob W._3

ljh, describe what is happening in the water gauge glass while the boiler is steaming? Are you getting a lot of movement? It may be that the boiler just needs a good skimming again.

ljh_2

no radiators were changed when I added insulation, nothing in the system was changed other than the boiler (and the near boiler piping) and the two replaced air vents. Wait - I did replace the existing seperate water heater. He added an indirect water heater (a super stor ultra.) would that make a difference? I assume the contractor added up the EDR etc - he measured every radiator # of columns, # of sections, height, etc.- I could ask him for that info (I guess I could get the book and do it myself - but that is why I hired a professional to do it - I'm handy but this really isn't my field) I just want to have a basic understanding of how things work so I don't make him come out to check something that ain't broke - and have him think I'm some annoying woman .....

dtc

Had similar problem when I replaced my boiler and solved it by increasing all vents by one size. 4's became 5's, 5's became 6's, 6's became C's, C's became D's. Sounds like your new boiler is too fast for its own good.

Jack P.

If you are building 2.5 lbs in 3 or 4 minutes and dropping back to .5 in one minute you must have a pretty small radiant field. That is the mains and radiators. Sounds like you are oversized just by that to me without knowing the EDR etc. How long does it take to build back to 2.5 lbs from .5 on the cut-out and cut-in. How many of those cycles in a normal maintenance burn before the stat is satisfied?

Long Beach Ed

JLH,

If all the radiators are cold when you start this thing up, I'm sure it takes longer than 2-1/2 minutes to get the farthest radiator hot. If the boiler is shutting down on pressure in 2 - 1/2 minutes without all the radiators being heated, then yes, you are short cycling. There is insifficent venting in the system and the air in the pipes and radiators is being compressed causing that pressure that shuts it down.

But -- if everything is hot, then all is fine. If the coldest radiator is filled with steam and hot ened to end the boiler has done its work and shuts down. Once some steam condenses the pressure drops and the boiler turns on again.

So if it's all hot, you are fine. But if it cycles on and off while portions of radiators are cold you have a problem.

Long Beach Ed

Joe_39

so what you are saying is that

AFTER all rads get hot all the way across it is normal for pressure to start to build and then boiler shuts down on pressure..

But, what is considered normal for this off again on again on pressure??

My system runs ,and it runs for a while (maybe 15-20 mins in morning after being off all night), then all the rads give off heat at the same time and all the way across, ptrol kicks in and shuts down at 1 1/2 -2 pounds of pressure, then it rests until presuure drops and she restarts for maybe another 2 to 3 minutes, over and over until tstat is satisified...

I always build pressure before stat is satisified, but I ALWAYS get heat evenly from EVERY rad in house

is this short cycling or normal operation??

soot_seeker_2

Its normal.