Boiler Short Cycling

Riley747

Hello All,

I am wondering if anyone can shed some light on a situation I have been having with my gas steam boiler. The boiler is a Weill-McClain (pictures below) rated at 150,000 BTU for a 7-radiator system one-pipe systems, and was installed in about 2011 prior to my ownership of the house. I have put a decent amount of work (replaced all air vent valves, radiator and mains (Gordon vents), skimmed boiler, reduced max pressure to its lowest setting, insulating pipes, replaced thermostat and set up properly for steam) over the past year and am now having problems with short cycling. The boiler seems to run fine until steam is produced and the radiators get hot, at which point the boiler shuts off about every minute on low water (I have sat in my basement and watched this happen with chagrin), and then the water refills fairly quickly and the boiler starts back up. The water level at startup and shut down is fine (a little more than half way up the sight glass). The house eventually gets up to temp, but it takes a while. I believe that I have dry returns (all return piping is above the boiler).

My concerns are:

1. The boiler is oversized for my system.
2. The the new boiler was piped inproperly (see pictures below)
3. There is a clog somewhere in the return piping.

I am having a pro come out to take a look, but wanted to know if anyone had any advice on this. Here is a link to the photos as the attachments are not working:

https://www.dropbox.com/sh/xijfpww077l8rgo/AADgd9jqIgrdgCy86kXbQEKua?n=110739032

nicholas bonham-carter

This could be the over pressure of the boiler forcing the boiler water up into the returns (1.75 inches for every OUNCE of pressure). Do you have a gauge showing ounces of pressure?
Also look for part of the return, which may be a little above the waterline, which could hide a lot of water, and then release it as soon as the boiler cuts off. This could even be some distance from the boiler.--NBC

Riley747

My Pressure gauge is basic, only in Lbs

nicholas bonham-carter

Find a 0-3 psi gauge either at valworx.com, or Amazon, and put it on the pigtail with the pressuretrol, to be sure.
They should come as standard with steam boilers, as every one here now has one.--NBC

KC_Jones

Couple things I noticed in the piping (all that duct tape makes it a bit confusing). It appears as though the riser connects to the bottom of the header. This is incorrect as any condensate coming from the system risers and the header will be trying to go back through that pipe. This could be effectively reducing the pipe size increasing velocity and sucking even more water out of the boiler. Also it's hard to tell what size riser is coming out of the boiler, but it appears a bit small. That boiler at a minimum is supposed to have a 2 1/2" riser coming off the boiler. Do you know what size it is? The smaller the riser the more likely you are to suck the water out of the top of the boiler. You should try adding a low pressure gauge that way you at least know what pressure you are running at. Just because the pressuretrol is set at a certain level doesn't mean you are actually running at that pressure they are notoriously inaccurate at the lower settings. Also it's hard to tell because of the angle of the picture, the Hartford loop connection looks a bit high. It should be at least 2" below the normal water line of the boiler. As NBC said this could be contributing to pushing water into the returns if it's too high.

Riley747

You are right, the riser connects at the bottom of the header (I had not ever thought about that), I think the riser is 2"

KC_Jones

If the riser is 2" it's undersized so you are getting too high of an exit velocity which will suck the water right out of the boiler. I would also take a loot at that Harford loop connection to make sure it's in the correct location. In case you don't have it here is a link to the manual for your boiler. All the recommended piping is in the manual, remember these are MINIMUMS and most pros on this site recommend going above that. It is good reference to see where you are. I think you actually have a Williamson of Thermoflo which is still a Weil Mclain, but for reference in the attached manual you have an EG-45 (150,000 BTU).
http://www.weil-mclain.com/en/assets/pdf/EG_Boiler_Manual_Series5.pdf

Fred

That header configuration/design could be a lot better. Also, the Hartford loop shold be a "Close nipple" maybe a couple inches. It looks like that has a 10" or 12 inch nipple on it. That will cause some noise too, even if it is the right height.
You may want to try skimming some more. Most boilers take several very slow skims before the water settles down. How many times have you skimmed it and did you use a skim port, above the water line and a very, very slow trickle to skim it?

Riley747

I skimmed it very slowly (2 hours) from a skim port about 3 times last year. I will purchase a 0-3 psi gauge (I have wanted to do this previously anyways).

Thanks a lot everyone for you help. Any thoughts on the oversized boiler? I am having a steam guy come out on Friday to access my options.

KC_Jones

Maybe I missed it, but what is your connected EDR that you think you are oversized? With 7 rads and a boiler that size it wouldn't surprise me if you are. Have you done all the calculations? That boiler can be fired at 125k BTU input as Weil Mclain actually sells that same block at that firing rate (I know because I have the lower fired one). If you are oversized that could be an option to replace the burner assembly with the next smaller one. Do the calculations and post them here and we could help you with this.

Riley747

We did the calculations and found that the boiler should be fired at 66k BTU, so it is 2x oversized.

wmtandson

nicholas bonham-carter said:

This could be the over pressure of the boiler forcing the boiler water up into the returns (1.75 inches for every OUNCE of pressure). Do you have a gauge showing ounces of pressure?
Also look for part of the return, which may be a little above the waterline, which could hide a lot of water, and then release it as soon as the boiler cuts off. This could even be some distance from the boiler.--NBC

for those of us not in the know can you explain
(1.75: per 1 ounce)

nicholas bonham-carter

When the boiler is cold, the waterline in the boiler, and in the vertical drop of the wet returns are at the same height.
As the boiler fires, and develops pressure, the waterline in the boiler is pushed down, and the water in the wet returns rises up with the displaced boiler water. This amount of rise is equal to 1.75 inches per Ounce of steam pressure.
This why we like to keep pressures as low as possible, so as to keep water in the boiler, and not store so much in the returns, during firing. Ounces of pressure are best.
Even if steam has not reached the main supplies due to bad main venting, this water movement will take place, as the air is being forced out of constipated little openings, which is why the venting must present as low as possible a resistance (back-pressure) to the escaping air.
Some installers, ignorant of this situation, will try to compensate by putting on a condensate tank, and feed pump, adding extra unnecessary things to break.--NBC