2 pipe steam boiler short cycling

ankeabu

First some background.

Dealing with my parents house which has a 2 pipe steam system dating from the 1900s to 1920s, unfortunately I don't have a firm date. The boiler, a gas-fired New Yorker model (pictures below), was installed in 1994, before they bought, and has worked well for a 20+ years of them living there with the whole system functioning quietly. The near boiler piping was done in copper, which we have been told by a previous contractor is improper but didn't require replacing. There is a single vent on the dry return near the boiler, it is a Hoffman number 76 (picture below). A little less than 20 years ago they a radiator in the kitchen replaced with a cast iron baseboard and a leaky valve replaced on a 2nd floor bedroom radiator. All radiators have the supply pipe on the top and the return side do not have steam traps. No service has been done in the last 15 or so years.

In the last week I replaced two other radiator valves, one on another 2nd floor bedroom radiator (that valve was stuck half open) and the other on a 3rd floor radiator (that valve had been stuck closed for at least 20 years and used to leak some steam.) As you will read below I was much less prepared for this project than I thought, although the actual valve replacement was uneventful. The original valves were made Adsco (I'll include a picture) and have removable orifice plates held in by a retention spring. The valves I replaced with turned out to be intended for hot water radiators (although I believed they were identical to the previously replaced radiator valve when I installed them.) Well the morning following replacing the valves I was awaken at 5am (when our programable thermostat begins calling for heat again after letting the the temperature fall overnight) by some wicked water hammer. I did some more reading on this forum and learned about the orifice plates and their essential function of keeping the the steam from making it down the dry returns. So I completely shut off the valve for the 3rd floor radiator and swapped the orifice plate from the old valve to the new valve for the second floor radiator. That fixed the water hammer.

However now we are having a different problem. The boiler is short cycling, rather extremely. It turns on when the thermostat calls for heat, flue damper opens, burner lights, water level in the sight glass starts dropping quickly, within about a minute the water level reaches the level of the Low Water Cut-off Switch, and the burner shuts off, damper closes, then opens and the cycle repeats. Overall the system is also much louder and there is some banging during the cycle although certainly not the water hammer from earlier. I noticed the water in the sight glass was very dirty (rust colored) and there was some sludge at the bottom. So with the boiler off I removed the petcock in the bottom sight glass valve and drained some water to get rid of the sludge but it just kept coming. So I stopped and refilled the boiler to nearer to the top of the sight glass so hopefully it would run longer cycles. Also important to note I never drained enough water for it to stop registering on the sight glass, a gallon or two at most.

Adding more water was successful in getting the boiler to run longer but were still only getting 5 minutes before it shuts off and starts over.

Knowing that I am now well out of my element we had a heating contractor who works on boilers come look at it this morning. He thought the problem may be that the burner is firing too hot and creating steam too fast. Which seemed odd as now adjustments have been made to the burner. But he didn't want to take on the job and said we needed a steam specialist and said he would give us a name if he could remember.

So my questions are:

What can be done to fix the short cycling? Is a flush of the boiler in order? Also the boiler manual mentions removing and cleaning the low water cutoff annually, should that be done?

Additionally knowing the valves I installed are wrong, is there a specific valve I should use? All the valves are 3/4".

Thank you all in advance.

EBEBRATT-Ed

Do you have any wet returns under the boiler room floor? Any water leaking anywhere.

ankeabu

Wet returns are a few inches above floor level. No leaks.

ethicalpaul

That’s not “short-cycling”. That’s “all the water getting carried or pushed into the mains causing the LWCO to trigger”

after 15 years the pigtail may be clogged and the pressure may be rising without the pressuretrol seeing it

Jamie Hall

Welcome! That has the potential to be a wonderful, even, quiet system. The potential.

It will work much better if you can get the pressure down to where it belongs, and to do that you will need to add a vapourstat in addition to the pressuretrol. That system will work best at a maximum pressure somewhere around 8 ounces per square inch cutout, with the cutin at 4. That's OUNCES.

As you are aware, the near boiler is ... actually not all that bad. No, it shouldn't be copper, and yes, it should be insulated, but the actual layout really isn't bad.

The Hoffman 76 is a wonderful vent, but it was meant to be used on coal fired boilers and really isn't big enough for oil fired boilers. I'd suggest swapping it for a Gorton #2.

ankeabu

Thanks for the quick responses! 

I just watched the boiler run a couple of cycles and want to make sure I understand what’s happening 

The boiler is shutting off before the water level in the sight glass appears to reach the level of the LWCO, is that due to the pressure rising too high? It only runs for a few minutes before shutting off and then restarting right away. That cycle repeats until the thermostat stops calling for heat.  If so how do I stop that from happening?  What seems odd to me is that there is nearly instantly enough water for the boiler to turn on again  

Makes sense about the pigtail to the pressuretrol being clogged, that loop of pipe seems perfect for collecting gunk. Is it as easy as removing it and checking that the pipe is clear? 

As for the vent. Sounds good about replacing for a Gorton #2. The current vent doesn’t seem to be opening nearly as often as it used to. And when it does it sounds like water is bubbling inside rather than just a release of air. 

Once I’m able to find someone who’s willing to work on the system I’ll get the Vapourstat installed. 

Thanks for the help! 

ethicalpaul

As you describe it this time, it does sound like it is cycling on pressure. Before it sounded like it was cycling on low water:

within about a minute the water level reaches the level of the Low Water Cut-off Switch, and the burner shuts off

There is a lot needed on this boiler and the causes could be multiple. Here are things I’d do:

- clean pigtail (you would disconnect conduit and the wires to be able to remove it) — replace with vaporstat

- install additional low pressure gauge

- flush boiler and returns of mud

- Flush the gauge glass 

- replace the main vent

- clean and maybe replace the LWCO probe

These things you wrote make me think water is getting in your mains. It could be because it’s dirty or due to high pressure:

there is nearly instantly enough water for the boiler to turn on again

And 

it sounds like water is bubbling inside rather than just a release of air.

Also we don’t know if the boiler is sized correctly (it sounds oversized) and the vaporstat could make it cycle even more. It looks like a big boiler—I wonder about the sizing of that single riser.

 On the bright side think of the maintenance savings over the last 15 years.

Gsmith

How about a picture of the piping between the boiler and the wall. Where is the water fill pipe to this boiler located?

ankeabu

Sorry for the confusion. Earlier on it also seemed to me to be cycling on low water but now appears to be due to pressure.

I definitely would like to flush the boiler and sight glass first as well as cleaning the pigtail, hopefully tomorrow. As for flushing the wet returns, that may be a bit trickier as there are no drains at the ends (there are two wet returns, one for each side of the basement, same for mains and dry returns.) The only drain is right by the boiler.

I'm adding a couple of labeled pictures of the piping around the boiler. Hopefully it is clear enough, it's hard to get it all in frame. The water fill connects into the vertical part of the one dry return where it connects with the dry return. I'm guessing this may make flushing the boiler difficult as there's no way to add water other than to the wet return.

ankeabu

Forgot to label. In view of the boiler from the front, above the dry return label on the right, is the location of the (only) vent, it is obscured in the photo by the main.

Gsmith

where does the wet return return to the boiler, I can't see it anywhere.

ankeabu

Here is a close up of the left side of the boiler. At the back is where the two wet returns meet and come forward to the drain valve. The vertical pipe connecting in is a drain from where the steam main splits above. The horizontal copper pipe connected to that vertical pipe
is the return to the boiler. It wraps around to the right side.

EricBaisch

Maybe there was oil on the new valves and it made its way to the boiler.  This will cause surging if the boiler.  You may just need to skim the boiler.

ankeabu

First of all thank you to everyone for the advice and answers to my questions.

This afternoon I did a thorough flush of the boiler and as much of the wet return as I could. Lots of rusty water came out along with some gunk. I filled and drained the boiler until the water ran clear. I also removed the pigtail to the pressuretrol and cleaned it out. A lot of gunk came out but it didn't seem to be fully clogged.

After refilling the boiler to the water level designated in the manual I turned the boiler back on. It heated up quietly and after about 10 minutes I was feeling heat in the radiators. But after running for about 15 minutes it shut off and began cycling on for 2 minutes, off for 2, so on. I noticed the air vent was spitting water again and the dry return was hot on that side of the basement. I traced it back to the return from the baseboard in the kitchen which was sending steam back down the dry return. So I shut that valve and the boiler stop cycling on and off, it stayed on until the thermostat stopped calling for heat.

The boiler has run a few more full cycles from the thermostat calling to heat without turning off until it stops calling. The water in the sight glass is staying very steady and the system is back to behaving nice and quietly like it used to. Thank goodness!

A new sight glass is in order and there are some more radiator valves to replace (but I'll be sure to swap the orifice plates over this time). Hopefully I can find a contractor in the area willing to work on this system in the near future to install some of the upgrades mentioned in earlier posts.


But for now I'm thrilled to have quiet, steady heat again.

Thanks again for all the help!

Jamie Hall

What, if anything, is on the return side of that kitchen baseboard? Bad trap? Can you put a trap on it, if there isn't one and you are depending on an orifice for control? Can you simply partially close the inlet valve and see if that helps?

ankeabu

There’s no steam trap on it now and I’m pretty sure there isn’t an orifice based on its behavior. I’ve closed the valve down pretty far. It’s open enough to allow the baseboard to heat fully without the return in the basement getting warm. I’ll look into adding an orifice or steam trap. Unfortunately it was was installed with copper and I suspect the joints were soldered after the valve was installed. 

Jamie Hall

Well, if the return is cool that's not the problem so don't worry about a trap or an orifice. The valve is controlling it. And the valve probably was put in before the pipes were soldered. Unions are cheap... you would think...