Steam boiler short cycling

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Old 10-06-14, 03:46 PM
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Steam boiler short cycling

I have an American Standard boiler G27 series 6B J5 with a McDonnell low water valve no.67 and an American Standard Detroit control valve no. 450. Last year the pig tail pipe between the McDonnell valve and the Detroit valve was plugged. I removed the pipe, cleaned it out and replaced. Since I have replaced it the pressure in the boiler does not get above 6psi thus the boiler seems to short cycle which is fine for heating the first floor but it takes forever to get heat to the second floor. Before the cleaning pressure would range from 12 to 15psi. Reason for the cleaning is the boiler would not fire no matter what the thermostat was set to. There are two adjustment screws or screw like things inside the Detroit valve, my guess is they need to be adjusted since the pipe is now allowing more pressure to get to the valve.

Dont know much about boilers. Any help would be appreciated.
 
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Old 10-06-14, 04:10 PM
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Hi Kevin,

First off I would like to recommend the best $25 you can spend on your boiler is this book:

We Got Steam Heat!: Dan Holohan: 9780974396002: Amazon.com: Books

This is REQUIRED reading for owners of steam heating systems.

Since I have replaced it the pressure in the boiler does not get above 6psi
You will learn from reading this book that you should never, ever need more than TWO PSI of steam pressure to heat your home. It's just not necessary!

The boiler should fire at a CUT IN PRESSURE of 0.5 PSI (yes, that's correct, NOT a typo, ONE HALF of a PSI) and should CUT OUT at no higher than 2.0 PSI.

If you can not heat your home with these pressures, there is something else wrong... venting, etc.

Where is the gauge located on the boiler? Is it on top of the siphon pigtail with the pressure control?

If not, does it clearly say on the face of the valve that it has an INTERNAL SIPHON?

Your gauge may be lying to you.
 
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Old 10-06-14, 04:29 PM
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I will defiantly pick up the book.

The gauge states internal siphon on the face and is located on the front top right of the boiler housing.

I have both range and differential on the control valve, I am guessing that the range is what you are calling the cut in. Right now the cut in is a little lower than 3 and the diff is a little higher than 3. I am guessing that I should lower the cut in to .5 and the diff I read on another post you recommended to be 1.5.

On item of note, the casting is cracked and the boiler leaks, no visible water is streaming out of it but you can see where a repair was attempted and obviously failed. Is this a big problem? The water valve will run once every 3-4 hours for a 1-2 second burst during the coldest time of winter (Detroit).
 
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Old 10-06-14, 04:38 PM
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I have both range and differential on the control valve, I am guessing that the range is what you are calling the cut in. Right now the cut in is a little lower than 3 and the diff is a little higher than 3. I am guessing that I should lower the cut in to .5 and the diff I read on another post you recommended to be 1.5.
I'm not sure with the old Detroit pressure controls. It could be that the RANGE is the 'cut out' and the DIFF is 'subtractive' from that.

DIFF can be either ADDITIVE or SUBTRACTIVE. The Honeywell controls that are typically used are ADDITIVE... I think yours may possibly be SUBTRACTIVE. I'll look and see if I can find something that confirms this.

With the settings you have, the boiler would CUT IN at 3 PSI and CUT OUT at 6 PSI if it's additive.

If subtractive, it would cut out at 3 PSI and cut in at 0 PSI... which might be the trouble.

Try decreasing the diff to TWO PSI and see what happens...

In the meantime I'm looking for your control.

Is this a big problem? The water valve will run once every 3-4 hours for a 1-2 second burst during the coldest time of winter (Detroit).
Yes, ultimately it can / will be.

Reason being that the constant addition of water brings with it minerals... hardness... calcium, magnesium, etc. This is going to 'scale up' the boiler. When that happens all kinds of bad things start happening.
 
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Old 10-06-14, 04:47 PM
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There are set nuts on the range side of the valve, if I screw the range all the way down to the stops it is at 1.5.

What is meant by cut in and out? I assume it means that the boiler will fire up at the cut in and shut off at the cut off. If this is true the boiler is always at 0 when not fired. I have a leak on 6" main union and two of the radiator control valves still leak a little, I repacked all the other radiator control valves and replaced the rubber stopper inside, yes I could have bought new ones but I like the look of the 1920's and yes I know I have issues.....a cross my wife has to bare.
 
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Old 10-06-14, 04:55 PM
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I couldn't find anything on that Detroit... other than the fact that there is a BA model and a BC model. The BC model is a 'vapor' control. I believe you have the BA ... it probably goes up to 10 PSI? I still don't know if it's additive or subtractive. Maybe one of our older timers will know.

When a steam boiler cools, yes, it will go to 0 PSI.

It won't fire at all of course if there is no call from the thermostat.

So, thermostat calls for heat ... if pressure is below CUT OUT, burner will fire and will continue to fire until CUT OUT pressure is reached. With thermostat still calling for heat, pressure will drop to CUT IN and the burner will refire ... etc ... etc...

Once thermostat satisifies, burner shuts off, boiler cools, pressure drops.
 
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Old 10-06-14, 04:56 PM
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How are the steam vents on the radiators? All functioning properly?

Are there vents on the MAIN LINE? (should be)
 
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Old 10-06-14, 05:06 PM
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I dont have any vents on any radiators and it looks like there never was any as I dont see any place for a tap. I do believe there are vents on the main. Looks like there is one on each loop just before the condensate drops back into the boiler.

On the control valve looks like the range is the cut in, hard to see the fine print but that is what the valve notes.

Understand about the cut in and out, makes sense. So if the cut in is at .5, I will adjust it down, what should I have the diff at?
 
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Old 10-06-14, 05:13 PM
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take it back it looks like there are plugs in the vent holes. I have two spots it appears, one half way down the side and one on the top. Do I need to put vents on all the radiators?
 
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Old 10-06-14, 05:19 PM
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Ummm... now again, I'm not sure...

Is this a ONE or TWO pipe steam system?

Can you post some pics of the piping around the boiler?
 
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Old 10-06-14, 05:26 PM
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I believe it to be a two pipe system. The hot pipe leaves the boiler then splits to two different directions. All the condensate returns via a cold pipe. On this cold return is the vent. I will post pics shortly.
 
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Old 10-06-14, 06:15 PM
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Not sure how to attach the photos.....
 
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Old 10-06-14, 06:20 PM
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Ok sorry for the upside down ect.....

The best photo has the insulated pipe 90 degree with the black return pipe next to it.

Photo 2 shows the two hot return pipes on either side of the cold return

Photo 4 shows the top cold return vent

Photo 5 is another angle of the hot and cold returns going into the main return pipe
 
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Old 10-06-14, 06:32 PM
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Two more wide shots. The return is on the back side. The first silver pipe is the hot return from the one loop, then the smaller silver pipe next to it is the cold return then the third pipe, hard to see is the other hot return.
 

Last edited by kevinaldi; 10-06-14 at 06:56 PM.
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