My Steam Boiler is Short Cycling -- Driving Us Crazy -- Help!

gerry gill

flushed out the boiler, and return piping? could be some chemical in the water causing this...could be firing rates to high..could be bad vents..not enough vents..etc.

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Jonathan Small

HELP -- My Steam Boiler Is Short Cycling -- Driving Us Crazy

Here's what happens:

Each heating cycle appears to have three five minute phases:

1. The boiler heats up for five minutes
2. The steam rises for five minutes
3. For the last five minutes, the boiler turns ON and OFF EVERY 25 seconds. So, it's ON/OFF about 10-15 times before finally turning off for good.

This happens all day long. It is driving us crazy. And it can't be good for the longevity of the equipment.

Last winter, Ed Wallace spent some time trying to figure it out, and he couldn't solve it. He tried a bunch of things -- perhaps he can share his experience and others can chime in.

Do you have any ideas? Can you help? I would appreciate any assistance in solving this puzzle. Thanks!

Ray M

Do you have a presutrol or vapor-stat?


Ray M
Comfort Tech Corp

tim smith

short cycling

Is it cycling on the low water cutoff or on the ignition system. It has to be one of the two and this is the 1st thing we need to know. ? water level bouncing causing low water to shut off burner or flame signal causing it. Let us know.

Big Ed_3

Oversized

Ten minutes all radiators are hot ? I guess first thing the boiler seems to be supersized . Oil or gas ? Type , make and size ?

For the short cycle , do you have any leaks ? Steam or condensate ? Auto feeder , what's it doing ?

What type and amount radiation ?

Jonathan Small

Short Cycling Steam Boiler: Please Help!

These are all good questions. I don't know the answers to all. I'm just a home-owner, don't really know much about all of this. See below:

The radiators are hot within ten minutes, although none of the radiators fills up completely. The first few sections get hot. Also, some radiators get hotter than others, so we've got the steam vents wide open on some and nearly closed on others.

It's a gas-fired Burnham boiler. The label says 245,000 BTU input. The house is about 3,600 square feet.

I believe there is a slight leak in the return line because the floor is a bit damp in one spot, nothing major.

We're definitely getting steam, but also plenty of noise in the radiators, so I'm sure there's condensation.

There is an auto feeder that appears to be effectively maintaining above the minimum water level.

We have old-fashioned radiators throughout the home -- I count 14.

Is it cycling on the low water cutoff or the ignition system? My assumption has been the low water cutoff, but I guess I'm not sure...how would I know?

Yes, the water level appears to bounce during the short cycling, but not a lot.

I have no idea on the presutrol or vapor-stat question...how would I know?

Thanks for taking time out of your Thanksgiving day for me...I am grateful!

Jonathan

Mark Wolff_2

oversized

Oversized is probably an understatement, depending upon construction quality. Heat loss calculations for your home will confirm that, but at first glance (68.05 btu per sq. ft) looks like it could be as much as twice as large as needed. Is it a new or older home?

Jonathan Small

Short Cycling Steam Boiler: Please Help!

How would oversize explain the short cycling?

Any of you guys located in the Boston area?

Thanks again!

Jonathan

ttekushan_3

Bad venting

in conjunction with an oversize boiler can cause a fairly fast rise in pressure, but by compressing air as well as steam. This could explain partially heated radiators.

But you're in Boston. So. if you have a nice drafty old home its not unusual to see the house heated at 45 BTU per square foot. So without even seeing the radiators (which you really need to measure correctly):

3600sf*45btu/sf=162,000btu

162,000btu*1.33IBR pick-up factor= 215,460 BTU OUTPUT required. If the steamer rating is 82% AFUE, for the purposed of this example 245,000 BTU*.82= 200,800 BTU.

This is not oversized. So when you go ahead and determine the style of your radiators and count sections etc, I doubt that you are going to find that the boiler is so grossly oversized that the short cycling is caused by the boiler size.

My guess is one or more of the following:
-contaminated water-or-firing rate way off causing massive water carryover into the steam lines-or-thermostat heat anticipator blown or electronic thermostat set for the wrong kind of heating system-

Terry

Todd_13

Check voltage at thermostat?

Had the same problem in my current dump, we got a deal on the house because of it. The thermostat was mounted on the staircase wall and had been nailed so may times by the disgruntled guys cleaning the house out that the wires were barely connected to it. I had about 9 volts getting back to the boiler, just enough for it to turn on, run for 3 minutes and shut off. Needless to say, no steam ever made it out to the rads.

Jim Pompetti

were to look

Find a professional , is your best bet.

DanHolohan

Here's a

LIST of things that can cause the problem you're having.

ed wallace

short cycling

Jonathons boiler has a very wierd problem I have replaced the electronic lwco on a temporary basis, jumped out the roll out switch,tstat and darm boiler still short cycles honeywell tech support was just about useless its not an issue of boiler being oversized yes water level bounces somewhat but never below the probe level my best geuss is a faulty honeywell smart valve that is not to smart

John Jette

steam system short cycling

Pig tail to pressuretrol may need to be removed and cleaned out.

Ed Wallace_5

boiler short cycling

pig tail cleaned,pressuretrol is fine,have jump out the safeties boiler dtill short cycles it has a mind of its own

Steamhead (in transit)

Ed, have you checked

the ground connection from the pilot/ignitor assembly back to the SmartValve? Most times this is thru the burner, manifold etc. back to the valve (or ignition module on other systems) and sometimes it looks OK but is erratic. An erratic ground can interfere with the flame-detection signal, causing the SmartValve to shut off the burner and attempt to restart it.

In cases like this I like to run a ground wire from the pilot/ignitor bracket to the ground terminal on the valve. Try this and see if it works, if so thank Tim McElwain for the tip. Also make sure the boiler itself is properly grounded thru the electrical system.

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ny homeowner

i had the same problem

I had a similar problem because my boiler is oversized. But I found through help on this board, that the thermostat was also causing the unit to short cycle. In my case, the home would heat up (all radiators got hot) and then the thermostat would cycle the boiler on and off and each cycle got smaller and smaller until eventually not all the radiators were getting fully hot. The electronic thermostat has an anticipator setting that is factory set for warm air furnace(setting 5) but can be adjusted up to 40. After back and forth adjustments, I found that if I left the temperature at the same setting, and adjusted the anticipator to a long setting (30 seems ideal), the unit would cycle in such a way that all the radiators got filled with steam and then thermostat shuts off just a little before the boiler would shut off on high pressure. I know in some ways this is less than ideal (as energy is consumed building up the head of steam) but this method does prevent excessive cycling and the house is very comfortably warn. I think in general using a setback thermostat on steam falls in the category of not worth it.

Steamhead (in transit)

If a steam system responds quickly

a setback thermostat will work well. Proper main venting and good dry steam are the primary influences here.

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Jonathan Small

HELP -- My Steam Boiler Is Short Cycling -- Driving Us Crazy

If this thermostat theory is correct, then the following test should work, no? During the short cycling, I raise the set temperature from 69 degrees (where it normally set) to 75 degrees. Shouldn't that stop the short cycling? It doesn't. The boiler is now pretty much going on an off every 20 seconds all day...HELP!

Jonathan

Jonathan Small

Hi Folks. It's one year later and I haven't been able to find anyone in Boston who can fix this problem. It's STILL driving us crazy. I swear: the thing probably turns on and off several thousand times per day. But just at the end of the heating cycle, once steam is being generated. I'm ready to tear the whole system out and start over...not really, but it IS that frustrating and annoying. Does anyone have any suggestions for a steam system expert in Boston who can solve this problem once and for all? Thanks SO much!

Jonathan Small

Still Short Cycling!

Hi Folks. It's one year later and I haven't been able to find anyone in Boston who can fix this problem. It's STILL driving us crazy. I swear: the thing probably turns on and off several thousand times per day. But just at the end of the heating cycle, once steam is being generated. I'm ready to tear the whole system out and start over...not really, but it IS that frustrating and annoying. Does anyone have any suggestions for a steam system expert in Boston who can solve this problem once and for all? Thanks SO much!

steveex

Try removing tstat, put r-w wires in wire nut, watch boiler for half hour, if it does not short cycle install a new white rodgers 1f80-0471, good luck

steveex

Try removing tstat, put r-w wires in wire nut, watch boiler for half hour, if it does not short cycle install a new white rodgers 1f80-0471, good luck

rob brown

short cycle

jonathan, it pretty much boils down to "is the call for heat being interrupted " as in voltage to gas valve dropping out, or is the burner dropping out, with 24 v constant to gas valve? if the latter, then a new flame rod ,or igniter,may be in order. or the dedicated ground steamhead spoke of. if the former, then a good tech with a volt meter should be able to track it down to the offending control.if the pressuretrol drops out, try widening the differential a little. if low water dropping out, check for proper mounting height of lwco and correct as necessary. i've also seen a mis adjusted anticipator on a t87 cause the mercury to slide repeatedly back and forth causing this situation. rob

Phil_17

short cycler driving H O crazy

i think it is about time that the manufacturers began to put the right sort of instrumentation on the boiler to help the H O make informed observations to report to the steam pro [or boiler factory]:
a pressure gauge that is suited to the job--0-3 psi
tell-tale lights on the vaporstat showing when off and on
same on LWCO to show low water conditions
ignition control lights
cars built at the same time as most of our steam systems usually had good instruments to determine the state of the engine-why not our boilers--for only an extra 1% of total cost?
it is certainly the H O who is johnny-on-the-spot to see what is happening with the system.unfortunately "how would i know" wont solve the problem.--nbc

bill_97

Sizing a steam boiler

by the sq ft of the home will give you nothing but headaches .

245,000 BTUs give out how many sq ft of steam ? Figure in 14 decent size rads and I'll bet the boiler is oversized by a factor of 2 . Maybe more .

bill_97

Ed

did you count up the rads to see if the boiler is the right size ? 14 rads on that size boiler sounds like way overkill . As a sorta loose guideline , we figure 10 rads for every 75 to 100,000 btus . Just a ballpark guess till we make a real count .

tim smith

Good call on thermostat

sometimes the simplest thing is overlooked. May just need to adjust the cycle rate on his existing thermostat. Hope this is his problem and he may be able to cure his problem himself. :O

Jonathan Small

Short Cycling

Ed Wallace, a pro who participates in these discussions, has already tried the following:
I have replaced the electronic lwco on a temporary basis, jumped out the roll out switch,tstat and darm boiler still short cycles. it's not an issue of boiler being oversized. yes water level bounces somewhat but never below the probe level my best geuss is a faulty honeywell smart valve that is not to smart. Also...pig tail cleaned,pressuretrol is fine,have jump out the safeties.
Plus, I have now tried replacing the thermostat with an "old school" honeywell round mercury style thermostat, just to see if this would fix the problem, but it didn't.

Jonathan Small

short cycling

As far as I can tell, the call for heat is not being interupted. The gas company tested the gas pressure, which is fine. What I really want is a recommendation for someone in Boston who can help me. THANKS

Unknown

Bauston area?

Sorry I learned that word from this site...
I thought there were several pros located in Boston area and none can help you? Perhaps this place would be a good location for steam wet stock...

Spudwrench

Assuming that Ed did in fact successfully defeat all the safeties & controls at the same time and it still short cycles- as others have said about the only thing left is the gas valve. Why not replace it? Even a non-steam HVAC tech should be able to swap out a gas valve. If you can't find a steam pro to do it, I bet you can talk a forced air type tech to do it, especially if you make it clear that you just want him to change the valve on your request and won't hold him accountable for the performance of the system. (i.e. if it doesn't solve your problem, you won't be complaining to him)

Good luck,
Nathan

Jim Franklin

Boston's a small town but geographically still a big place. What part of Boston are you in? Someone otherwise completely booked might find out you live a block away and come have a curiosity look one night.

jim

Ron9

Help

Did you ever thin k that the nozzle may a bit too big for the heat load? Try downsizing the nozzle.

Jonathan Small

Short Cycling Solved!

Hi Everyone who has been following or contributed to this thread. I wanted to let you all know that my problem has finally been solved. The cause of the short-cycling was low gas pressure. We had 9 column inches of pressure while stable, but it dropped down to approx 4 or less when the system turned on. It turns out that there was some blockage in old rusty gas lines and a slight leak at the T in the street leading to the house. After an all-day event with the gas company, the problem is solved, and there is no more short-cycling. Thanks to everyone who volunteered their thoughts and time to help (you know who you are). I really appreciate it.

Jonathan Small

John_205

can you tell me what a vapor stat is ??

thank you

Brad White_185

A Vaporstat

is just like a pressure-trol, operating the boiler to a specific range (cut-in to cut-out pressures). Pressure-trols have a range of from 0.5 PSI to 5 PSI or more.

A vaporstat has a much smaller range, often in ounces. 0-16 ounces and 0-32 ounces for example, with even finer differential settings than a pressuretrol.

These are the only real practical way to control a steam boiler consistently in those nice low ranges we crave.

tim smith

That's why we carry digital & u tube manometers

Congratulations. We try and get our guy's to test gas pressure when they are doing annual maintenances. We test combustion, so gas pressure is a good tool also. Tim