Pressuretrol problems?

cdm

System seems to work normally @ 70 degrees and 0 psi. (pressuretrol is set @ 0.5 low + 1.0 high). When I raise temperature  to 72 degrees, the pressure rises to 2.25 lbs. - temperature  @ 72 degrees, and boiler goes off.  When  pressuretrol drops to approximately 0.5 lbs. the boiler comes back on, and pressuretrol goes to 2.25 lbs. - boiler then goes off - temperature remains @ 72 degrees. This sequence will repeat until temperature reaches 73 degrees - then  boiler goes off.  It seems as though the pressuretrol is the problem?  Maybe  the Honeywell thermostat sensitivity is off?   What am I missing here ?



cd mulford

Hap_Hazzard

The pigtail?

Your pressure is probably being limited by the rate at which the radiators condense the steam. When you raise the temperature, you are making the boiler come on before the radiators have cooled completely, so they can't condense the steam quite as fast, so the pressure runs a little higher.



My guess is that your pigtail has become plugged so the pressure isn't reaching the pressuretrol, so it can't 'trol your pressure. As long as your pressure isn't getting dangerously high, you don't need to treat this as an emergency, so your first step is probably to order a new pigtail (a brass one) so you'll be able to replace it quickly.

Boiler Talk

I don't know, but it sounds like its working

How old is the pressuretrol?  It sounds like it is operating, but not at the settings you want.  I saw this type of action on my boiler after a large setback.  That is, I wanted to go from 65 degrees to 69 in the morning.    Is this what you are doing?   I found like many others that pressuretrols are poorly constructed, but can be adjusted .... somewhat. 

BobC

Not precision equipment

Pressuretrols are not precision devices and a 30PSI gauge is not at all accurate at one or two PSI. You would need a low pressure gauge (0-3 PSI) to determine what the pressure really is and then you are still left with the idiosyncrasies of the pressuretrol.



Bob

JStar

Steam

How often does it cycle? How long is it on? How long off?

cdm

Pressuretrol?

Thanks for the response - I recently cleaned the pigtail and put in new plumbing , sinse I added a 0-5 psi gauge.  Your reasoning really makes sense as to why the pressure is rising - never considered that!



thanks again -cd mulford-

cdm

pressuretrol?

I am only raising my temperature from 70 to 72 degrees, but I think you are probably right about the set-back (65 to 70 degrees) showing the same pressure response in the morning.  I will check this out tomorrow.



thanls -cd mulford-

cdm

Pressuretrol?

As i mentioned, I do have a 0 to 5 psi. gauge along with the 0 to 30 psi gauge and the pressuretrol.  I am really surprised that the 30 year old 0 to 30 psi. gauge) actually indicates a pressure very close to my o to 5 gauge pressure. Thanks for your input.



cd mulford 

cdm

Pewssuretrol?

The cycling usually is twice (ie.)  Long cycle to bring house to 72 degrees, then off for approximately 5 to 10 minutes, then on for 10 minutes. This last cycle wll repeat for one or two more times until temperature reaches 73 degrees - then boiler goes off.  If I interupt  the cycle by raising the temperature to 73 degrees - the boiler will go off.



cd mulford

nicholas bonham-carter

Short-cycling problem

This on-again-off-again behaviour is coming from either the thermostat, or more likely from inadequate main (not rad) venting. The mains should be vented generously so that air escapes with no resistance ( low back pressure) as the system first starts to make steam, look at your low pressure gauge, to see the back-pressure of venting, and it should be below 2 ounces until steam reaches the main vents and closes them, at which time the pressure may rise if the boiler is over-sized. This fills all the mains before any of the risers begin to feed the rads. If your radiator vents are too large, then replace them with Hoffman 40's.

As far as the thermostat is concerned, some older ones will have an anticipator which when set wrongly can cause short-cycling. The newer digital round honeywells can be set for steam, and do a good job. If you put a jumper on the terminals attached to the thermostat to simulate a call for heat, your testing will be for the boiler only. Start your back-pressure measurements in this way.--NBC

Just thought of another possibility:

If you try and adjust the standard pressuretrol down to the lower settings, the linkage can become unhinged, and then it will allow the pressure to rise out of control (in my case to 10 psi!!!) these standard issue pressuretrols are the work of the devil, and only useful for holding the installation manual open, so get a vaporstat.

cdm

pressuretrol?

I installed main vents sized for 3oz. pressure relief, but 'the wall' suggested venting @ 1oz. - so I am installing additional main venting that calculates @ 65% over-venting. If there is such a thing as over-venting mains. I have new adjustable Hoffmans on all radiators and all rooms normally heat evenly. I have wondered about installing a vaporstat - any suggestions on one?



thanks for the input -cd mulford- 

MTC

What length/size are your mains?

and what vents do you have on them? If you're sized to vent out at 3oz in 1 min, you shouldn't really "need" more venting, it would just be a bit more optimal. I don't think this would be causing you to short cycle on pressure.



have you done an EDR calc on your connected radiation, and compared that to the rating of the boiler? It kind of sounds like your boiler is just significantly oversized, a common problem.

cdm

Pressuretrol?

2 Mains : One 2" X 28" with 1 Hoffman #75 - soon to be replaced with 1 Gorton #2.  Second main 2" X 38' with 1 Hoffman #75 - soon to be 2 Hoffman 75s and one Gorton #1.

This should be approximately 65% over venting at 1 oz.  Radiator EDR = 236 sq.ft. add in 33% for extraneous plus piping equals 75,300 BTUs.  Present furnace a Weil Mclain produces 320  ft steam or 76,800 BTUs. So I think I am OK on boiler size.  I should know how I stand in a few days if venting changes were effective or not.



thanks for your input  -cd mulford- 

MTC

Sounds like a plan

see how maximum venting works out for you, and go from there. You might be a bit oversized there, especially if your piping is insulated, but not drastically so. Def better than a lot of the monster boilers out there...

nicholas bonham-carter

Testing results

Have you been able to jumper the thermostat terminals (not set it up), and if so did the short-cycling continue?

What was the pressure during the venting stage during this test?--NBC

Boiler Talk

The clunky pressuretrol - Lowering the Pressure

Maybe a picture of the pressuretrol can help.  My unit is an additive type.  It has a Cut-In scale on the outside.  It's set to 0.5 lbs on this scale.  There is a wheel with numbers inside.  The wheel is part of a switch that turns off the boiler when the pressure in the system pushes up the rocker upon the switch.   The wheel has number 1 to 5 on it.  That means 1-5 PSI cut-out.  This not a precision instrument.  The position of the switch was several fractions of an inch higher than it could be.  Before for doing anything, be sure to turn off the power.  I lowered the switch to obtain a better Cut-Out pressure.  Again, the switch was positioned so high that the measurements shown on the scale and wheel meant nothing.  I was getting cut-out at 4 lbs even with the wheel set to 1 psi and the Cut-In scale spring set at 0.5 lbs.  I tried bending the Cut-In Scale indicator upward to obtain a lower Cut-in, but I think this matters less than the switch position.  I made sure that cut-in screw was firmly attached to the spring on the other side of that rocker system.  A picture? 



I got rid of the large swings in the temperature.  It's more comfortable and I don't see the pressure rising crazy like it did before.  Adding main vents was key for me.  I am saving fuel. 

cdm

Pressuretrol?

NBC - Thermostat is a Honeywell 3600 (battery powered), so when I remove the face plate to access the terminals , there is no voltage applied at the terminals - so there is no difference when I short the terminals, with or without steam pressure.  I did increase the venting yesterday - but no change in steam pressure.  Still goes up to approximately 1.25 psi on a temperature rise (65 to 70 degrees) from the night time set-back.  When I go from 70 to 72 degrees, the pressure rise goes to 2.25 psi.  That seems to be the maximum steam pressure the system sees.  I opened the pressuretrol - the outsude is set @ .5 and the inner wheel is set @ 1.  I can't go below 1 by more than 1/8" measured at the outside of the inner wheel.  I think you are right - the pressure is due to little further condensation of the steam since the radiators are already hot.   I am thinking the pressuretrol is the problem.   Any suggestions?



thanks -cd mulford- 

nicholas bonham-carter

shorting the thermostat

the thermostat is only a temperature operated switch. when the temperature falls below the set-point, the switch closes, and vice-versa. shorting the terminals at the boiler will effectively remove the thermostat from the circuit as a cause of short-cycling.

once i got my pressuretrol replaced, i was able to keep the pressure in the ounces range, with lots of main venting. your boiler may be over-sized, and therefore the cause of cycling.--NBC

cdm

Pressuretrol?

NBC : I got to thinking about the thermostat leads to the furnace.  These leads terminate at a terminal board on the burner.  I shorted these terminals and the burner ignited.  If i do the same when the steam pressure is @ 2.25psi what should I expect to happen, and what will this tell me?



thanks again -cd mulford-

cdm

Pressuretrol?

Thanks for the input - It does sound like a pressuretrol problem, as I just increased main vents to approximately 65% greater than what is needed to vent 100% at 1 oz. steam pressure.



thanks -cd mulford-

nicholas bonham-carter

Diagnostic procedure

Jump the terminals, and let it run. Have a look at the gauge while it starts to make steam, and see if it stays below your 3 ounces, while the air is escaping.

With the terminals shorted out, you can see if the short-cycling continues, (the thermostat now is not in control, and therefore not the cause). This leaves the lwco, or the pressuretrol as the causes of cycling.--NBC

Hap_Hazzard

Fine adjustment

Rather than moving the switch to get a more accurate setting, you can adjust the push rod that connects the rocker to the diaphragm. If you look closely at the end of that threaded shaft you'll see a hex socket that accepts a very small hex key. (I can't remember the size offhand, but it's small.) You can't change the differential, but you can set the cut-in.

Boiler Talk

Pressure cut out - Large temperature swings

CDM



I left out an important point in my note above, which is the switch inside the Pressuretrol is not precisely mounted.  Again, if you were to loosen the two screws that are used to fix the switch's position, you would likely find the switch can be moved up and down.  In your case you could push the switch down and I bet you would obtain lower cutout pressure.  Doing this will not stop short cycling.  If I recall correctly, you have a large temperature swing of almost 5 degrees.   Lastly, if you had only a 3 degree change, its possible you might not see the short cycling.  Best of luck.