Short Cycling and High Pressure after a few weeks of warm weather?

Bcos17 · May 22

Hello all,

We've had warm weather recently (Northern NJ) and so my heat has been off for the past few weeks. Prior to the season ending, my 1 pipe steam system was running perfectly, the 5 PSI gauge never registered anything above 0 and my system would run for 15-20 minutes once an hour or so. Over the last few days we've had colder weather so I decided to turn the heat back on. Internal temps were 62-63 degrees, and I set the thermostat to 69.

What has happened now is that my system is short cycling and my pressure is spiking. I also have a hot water boiler in the same basement operating an addition to the house. That boiler is on and thermostats are calling for heat, but the boiler is not running. Occasionally the exhaust fan will start for a few seconds and then shut off. The Grundfos circulator which is normally dark when not running is on and registering 0 gallons per minute.

Does anyone have any idea what might be causing these issues? Could they be related? The steam system has an abundance of main venting and the pressuretrol is set almost as low as it can be, so I'm not sure why the steam pressure is rising, and I cant figure out why the hot water boiler wont run properly.

Thanks in advance for any ideas or suggestions you have.

Jamie Hall · May 22

Disconcerting. The two issues may be related, as it almost sounds as though there is an electrical or rather wiring problem which is keeping the hot water boiler from running when it is asked to — and another, or related, one which is interfering with the control from the pressuretrol.

Without really looking at the way the controls are arranged, it might be hard to trace…

EBEBRATT-Ed · May 22

I would take the pressure control on the steam boiler off and make sure the control, the pigtail and the pipe connecting the pressure control to the boiler are clean.

Someone did a really nice job piping that boiler.

With the HW boiler is sounds like the exhaust fan is not being proven on by an air pressure switch. Usually the fan will start, the pressure switch will prove the fan is running and allow the burner to start.

ratio · May 22

Any chance that some valves got closed?

Bcos17 · May 22

https://forum.heatinghelp.com/discussion/comment/1856146#Comment_1856146

You got it. I cleaned out the Magnaclean and forgot to reopen the valves 😮. Very dumb on my part. Still trying to figure out why the Steam boiler is developing pressure.

ratio · May 22

A valve closed on the steam system would explain things there as well…

Bcos17 · May 22

I didn't touch the steam at all and I dont have any valves on the supply pipes. Main vents and radiator vents havent been touched. The only thing that is different is that the system was trying to heat up from 61 degrees as opposed to a normal 2-3 degree variance.

ratio · May 22

How soon did the steamer start building pressure after it fired from a cold start? The next simplest explanation is oversized, but it's a pretty tight window to be oversized enough to short cycle on an 8° recovery but not build any pressure during normal operation. Try a slower recovery (2° every few hours or so) & see what happens.

mattmia2 · May 22

Someone did a lot of work for it to be oversized. Do all the emitters for the steam system heat? Some of the system not heating because valves on radiators are closed or piping is holding on to the extra condensate from the setback or some venting is clogged would make it build pressure even if it is sized right. Are you sure the gauge is accurate? The gauge and pressuretrol seem to be on the same pigtail. What is the differential set to on the pressuretrol? Is that a version with an additive differential?

Bcos17 · May 22

It started building pressure pretty quickly from a cold start, maybe 5-7 minutes. It's slightly oversized but not too bad. All of the radiators heat, or at least they did 2-3 weeks ago. No valves have been touched. The gauge is definitely accurate. The differential is set to 1 on the pressuretrol. As I said earlier this is very odd because I had it absolutely dialed in all winter, pressure was basically 0 or unreadable on my 0-5psi, and it was working flawlessly. I gave the main vents a tap just in case something was stuck. I can't figure out what else it would be.

ratio · May 22

Can you feel steam in any of the pipes? Maybe pull the vent from the radiator closest to the boiler & see what happens.

mattmia2 · May 22

I'm thinking there is a slug of water somewhere but I can't figure out how that would make more than a few ounces of pressure.

where is the water line in the sight glass? does it move as you would expect?

pedmec · May 22

is it heating the radiators before it cuts out?

neilc · May 22

I think you need to back up and ask why the Ptrol isn't cutting out before getting to 4 psi,

Bcos17 · May 22

It short cycled for an hour or more, on and off every few minutes, and the house warmed up to the high 60s before I shut it off. The radiators were warm.

Neil, I think you make a good point, but im confused why it would be working a couple weeks ago and now be clogged. I'll take the pressuretrol off and clean it, ditto for the water seal, and see if it makes a difference.

Matt, the water line was slightly lower than I usually run it, maybe 1/2 to 1 inch lower in the sight glass. The reason for this is that I drained some water from the site glass and the lowest drain to get any sludge out after I thought we might be done for the season and I didnt want to add any oxygenated water if it was going to sit all summer. I added some now and put it back to the regular level.

Thanks everyone for the ideas.

mattmia2 · May 23

i was wondering if the fill valve, whatever form it has, was leaking at about the same rate as normal water loss and it was now flooded after not operating for a while but that doesn't seem to be the case

Bcos17 · May 23

No, definitely not leaking. I redid all the water feed piping a few months ago and added the demineralizing filter. The water level was steady, albeit just below where i normally operated it.

Bcos17 · May 23

I just turned the Steam Boiler back on after sitting cold for several hours. After adjusting my water level back up to its usual place (marked by the blue painters tape on the metal rod next to the sight glass), the pressure issue is gone. It's currently about 20 minutes into a heating cycle and the pressure hasnt moved above zero (vs 4 psi earlier today). Is it possible that the water level being a little lower earlier in the day (Approximately the red line) was too close to the hartfood loop and that was causing the pressure to rise and the boiler to short cycle? Looking back at my copy of the Lost Art of Steam Heating, it indicates that my water level should be 2 inches above the top of my street 90 on the hartford loop. I don't think I have ever had the water that high, it looks like my standard level is about 1/2 inch above the top of the street 90. Based on this, I think I should move my standard water line another 1.5 inches higher, right around 3/4 of the way up the sight glass. Sound right?

mattmia2 · May 23

do yo have buried returns? are they leaking? if they are dry then steam could follow them to the end of the mains to close the vents before the mains were vented then that would cause your pressure issues.

there are other permutations of that too but the general idea of losing a water seal somewhere and following a return to the end of a main and closing the main vent before it vents the main will cause a bunch of the system to not heat which will take that load off the boiler and make the pressure go up. It is more common to happen where 2 drips connect together and a new boiler lowered the water line and made the connection to the return no longer under the water line.

Bcos17 · May 23

Not buried, wet returns but not leaking, they run along the floor of my basement about 2 inches off the ground. This has to have been the issue, but I don't understand the mechanics of why it caused the pressure to build so quickly.

mattmia2 · May 23

https://forum.heatinghelp.com/discussion/comment/1856234#Comment_1856234

the steam short circuits the main through a return

that steam heats and closes the main vent

the main is still full of air so the radiators aren't heating

there is nothing to condense the steam the boiler is producing so it builds pressure (the pressuretrol not cutting out is another issue)

eventually the main vents through the radiator vents and the radiators start to heat and consumes the steam from the boiler at the normal rate

(this is one pipe, right? it can happen with 2 pipe too but the mechanism is slightly different)

EBEBRATT-Ed · May 23

All the boiler mfgs want the Hartford loop 2"-4" below the boiler normal operating level. That is measured to the bottom inside of the horizontal nipple.

The normal operating level is considered to be 1/2 the gauge glass unless marked otherwise by the boiler mfg. The install manual will show this.

Camera angles can be deceiving but yours looks about right. Since the installer did a nice job piping i bet he got it right.

mattmia2 · May 23

i bet there is some old return connection out in the system that isn't as far below the water line as it was with the original boiler so it causes an issue when the boiler is a little low.

109A_5 · May 23

Lower the boiler water level to where it was before and see if the issue is repeatable that way.

ethicalpaul · May 23

How did the water level drop to that low level, just from normal usage, or was it sudden?

mattmia2 · May 23

https://forum.heatinghelp.com/discussion/comment/1856293#Comment_1856293

I think somewhere in there the op said they drained some water out tryign to flush something out but didn't want to add fresh water without heating it to drive off the air

ethicalpaul · May 23

ok thanks. Misguided belief about driving the O2 out I think but that explains the level.

Bcos17 · May 23

Hi Paul,

I thought I've read that you should run a heating cycle at least after adding any water to get rid of any oxygen, is that wrong? I drained some water to get rid of any last sludge/rust before summer. There was minimal rust because I keep my PH around 9-10, but the result of draining some water was that my sight glass level was lower than normal. I thought the boiler was going to stay off through the summer, so i didn't bother to add any water because I didn't want to add oxygenated water and I didnt feel like running a heating cycle as temps were high at the time. When I restarted the boiler this week because of the lower temps we've been having for a few days, i did so without adding water and i started having my pressure issue. Once I added water back to my normal 1/2 way up the sight glass level, the boiler went back to running at almost 0 PSI.

mattmia2 · May 23

if you heat it to just boiling you have heated it enough to drive the dissolved air out, you don't really need to heat it to a full cycle. if you put some water on the stove to boil, you will see little bubbles forming in the pot a while before it boils. those bubbles are the dissolved air. It mostly comes out of solution before it reaches boiling.

ethicalpaul · May 23

I thought I've read that you should run a heating cycle at least after adding any water to get rid of any oxygen, is that wrong?

Yes I believe it doesn't help. Here is why:

boilers rot out in the steam chamber. They do not seem to rot out below the water line. If oxygen staying in the water longer was a problem, we'd see the rotting happening below the water line.
If boiling the water quickly after adding it did reduce the corrosive effects of oxygen, then we wouldn't see boilers rotting out from too much fresh water because in almost every case, the water is boiled soon after it is added (because it is added during a call for heat by an auto-feeder).

What I believe happens is that regardless of when the O2 is driven out of the water by heating, that freed oxygen goes into the steam chamber and attacks the metal above the water line, eventually rotting a hole in it.

If you really want to reduce the corrosive effects of makeup water, you can pre-heat the water before adding it to the boiler.

Short Cycling and High Pressure after a few weeks of warm weather?

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