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Old 05-14-2010, 11:16 AM   #1
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Steam boiler is short cycling


New steam boiler (Burnham Independence IN5) in my 100-year old house goes through 25 on-off cycles to raise house temp 3 degrees. Installation contractor is not concerned. I'm leery of his advice. Does this extreme short cycling need to be fixed and how should it be resolved? Details: 2-pipe steam system, 10 radiators, Vaporstat set at 14oz max - 7 oz min, Honeywell classic round non-programmable thermostat. Please advise.

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Old 05-14-2010, 04:32 PM   #2
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Steam boiler is short cycling


Just a guess.
The contractor installed the same size boiler as was there. And the new boiler holds less then half as much water. So it gets to pressure much quicker. And also drops pressure much quicker.

He should have checked the amount of radiation you have. And sized the boiler by that.

Next possibility, is that you have a bad steam trap. Or a leak in the return line.

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Old 05-15-2010, 09:57 PM   #3
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Steam boiler is short cycling


The old boiler had been converted from coal to gas, probably 50+ years old. There was no way to determine its BTU output (I think). If the new boiler is improperly sized, what's the solution, short of replacing it as well?

The contractor installed a new steam trap. Does a heating system typically have more than one?

There does not appear to be a leak in the system.
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Old 05-15-2010, 10:14 PM   #4
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Steam boiler is short cycling


Depends what type of set up you have. You could have a trap on each radiator.

Contractor should have checked the size of your radiation. And sized to it. Doesn't matter what size the old boiler was. The radiation is supposed to be checked before installing a new steam boiler. To help prevent things like this from happening.

That boiler holds less then 8 gallons of water. Your old one probably held 30 to 40 gallons.

The new boiler provides steam much quicker then your old one did.

About the only thing you can do. Is set the on pressure lower. Set it to 3oz. That should cut out 20 to 40% of your cycling.

Other then that. A new CORRECTLY sized boiler is the answer.
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Old 05-15-2010, 10:20 PM   #5
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Steam boiler is short cycling


PS: Might want to check for a main vent that doesn't close.
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Old 05-16-2010, 07:34 AM   #6
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Steam boiler is short cycling


You should only be running about a half a pound of pressure anyway but, if the boiler is oversized you can down fire it also.
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Old 05-16-2010, 07:46 AM   #7
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Steam boiler is short cycling


Can't safety lower that boilers firing rate lower then 128,000.

And he'll still be short cycling.

One other thing he should check though. Is if its short cycling off its vaporstat. Or its low water cut off. If its the cut off. Then he ha a problem with his return piping. Could even be something wrong with the trap.

If not. He's stuck with the wrong size boiler.
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Old 05-16-2010, 08:49 AM   #8
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Steam boiler is short cycling


Yep, and he didn't say if he has wet returns or not. they get plugged up. This sort of thing happens all too often when someone that doesn't understand steam changes out a boiler. New boilers make steam a whole lot faster than the old beasts did. If you don't take the time to size to the radiators you will have problems 9 times out of 10.
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Old 05-16-2010, 08:53 AM   #9
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Steam boiler is short cycling


Yep. Too many swap same size for same size.

And never look at anything thing other then the boiler BTU size.

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