Low Water Cutoff Constantly Interrupts Cycle

Steamed

The low-water cutoff on my residential steam boiler constantly interrupts my steam cycle.  From a cold start, the boiler fires, the water slowly drops, it gets below the LWC sensor in the boiler (it's low in the sight glass but not at the LWC line yet) and the boiler cuts off. I shut the auto-water feed off so the boiler doesn't auto-feed and overfill.  The boiler cools for about a minute, then condensate comes back in quickly (about 3 minutes) and the boiler starts back up.  It keeps doing this until the thermostat stops calling. The radiators heat correctly. Pressure doesn't build up in the system until after about 45 minutes of cycling, after the radiators are heated, and never gets above 0.5 psi.  Please help me solve this problem so this thing can cycle efficiently.



Here are some details on the system that may help:



- Single pipe system

- Near boiler piping is single output, piped according to boiler specs.

- 28" from boiler output to header

- Header supplies 2 mains, which appear to be pitched correctly

- 3 Gordon #2 main vents at the end of each main.

- 8 radiators, varying in size from 12 fin to 20 fin; each vented with a Heat-Timer Varivalve





Here are things that I DO NOT think are causing the problem:

- surging - the sight glass level doesn't move more than a 1/2 inch and it looks dry above the water line, so i don't think oil or surging is the problem

- undercapacity of the boiler - I've calculated capacity and it seems to just fit the system; also, if it were undercapacity the water wouldn't come back in so quickly after a cutoff, it would be out in the system and take longer to come back.



I thought the problem might be steam pressure angling the boiler water below the cutoff sensor, but a steam heating specialist that checked the system didn't agree because the boiler was piped as spec'd by the manufacturer.  That specialist suggested that I replace the radiator vents because they probably weren't letting enough air out, which was creating pressure on the water in the boiler and pushing it below the cutoff.  I'm having a real hard time buying that. Varivalves vent really fast and I don't get how that could impact the water in the boiler.



I've been researching this stuff for months. I've got Dan's book. I know way more than any homeowner should know about this stuff. Please add your thoughts to my madness.  Also, if you can recommend a really good technician in Bergen County, New Jersey, I would appreciate hearing about them.



Thanks,

Leo

ChrisH

Check your return pipes

Usually the problem is that the return pipes are clogged. (just the horizontal part in the basement). They do not allow the  water to return fast enough back to the boiler. 

Steamed

Check you return pipes

But if it were the return pipes, then wouldn't it take longer than a couple of minutes for the water to come back into the boiler after it cuts off? It seems to refill pretty quickly. Any way to test that without taking the return pipe apart? Thanks.

crash2009

What model of boiler do you have?

Is it one of the boilers that are very picky about their water line?  Waterline distance from the floor.

ChrisH

It depends on many things

But if we are talking for a regular size house with 80 year old return pipes then they are clogged

Jamie Hall

Have you checked

the settings on your auto feeder and LWCO?  Some types (the newer ones) have a provision for a variable delay on the feed, at least.  Might try a longer delay...

Sil

I am no pro....

But I had a similar problem as you have. Feeder would kick in sever times each cycle.



I tried everything... but at the end of the day, I replaced the wet return lines in October. Since then, my feeder has not kicked in once.

nicholas bonham-carter

mysterious water-level disappearance

could you have a part of the return piping which is slightly above the boiler waterline? the pressure of the boiler will push down on the waterline, until a point of equilibrium is reached, and that point with a bit of horizontal return may be "hiding" your water. congratulations on having an accurate gauge to monitor the pressure.

the area in which to look for this horizontal element which is to blame, would be the pressure, in ounces, multiplied by 1.75 inches. look above the waterline that distance and you may find the culprit.--nbc

jpf321

please send pic

of your LWCO arrangement at boiler .. we saw one here recently that was installed higher than it should have been because they used an elbow they shouldn't have .. also, have you considered slightly overfilling boiler? it only matters significantly until some steam is in the system and the waterline falls to "normal" perhaps you can find a happy medium between overfill and LWCO interruption (although you shouldn't have to) ..



please send those pics.

The Steam Whisperer (Formerly Boilerpro)

Two things.....

Some models of LWCO's are designed to shut the boiler down at a set time period to check for water foaming.....see if you model is one of these. 

Your steam specialists's concept of the pressure pushing down on the boiler water doesn't hold water.  However, if your venting on your mains is too slow, the steam will take alot longer to get to the end of the main.  Therefore, the water will return slower.  Fast radiator vents will not correct this problem, and will likely make it worse, since they tend to cause the first radiator off the main to fill with steam, then the next, and the next, progressively down the line.  Steam moves much faster than water through the system, so let it get to the end of the main and start condensing in the last radiators quickly.  This will also make the hime heat more evenly ( a well balanced steam system willheat  all the rooms within about 1/2 Degree Farenhiet).   The steam should reach the end of the mains within  a minute or two after the boiler header gets hot on a typical heating cycle.

Steve_175

Main Vents

He said he has 3 Gorton #2's at the end of each main. That should be plenty of venting I would think. Maybe part of the Hartford loop is clogged (assuming he has one)?

Charlie from wmass

how about closing those

vari vents down by half. I would say you are actually venting too fast. Photos of the boiler may help but I am thinking you are slinging the water out the boiler and up into the radiators. Yes I know I am the anti vari vent guy by now but I just do not like them.

Charlie from wmass

also what make and model of boiler

do you have. As Boiler Pro said some model shut down on a schedule to cut down on foaming.

Steamed

Answers to your questions - thanks

Thanks for all the advice. I really appreciate it. Here's some answers in order of your posts:



Chris H - Any way to check if it's the return pipes without taking them apart?



Crash2009 -  Pennco 1604 HSD - http://www.ecrinternational.com/secure/upload/document/980.pdf

I don't think it's picky about the water line. It seems pretty steady and seems to fire and work fine until it sinks too low and cuts out.



Jamie Hall - I turned off the auto-feeder to avoid an overfill. It does have a longer delay setting and I can use that, but the auto-feeder isn't an issue for me. I'm focused on solving the cycle interruption.



Nicholas - I'm not to clear on your comment. All of my return lines are above the boiler water line until they go vertical to the floor.   Yeah, I installed a new gauge after many visits to this site, as it seemed pretty essential to diagnosing some things.



JPF321 - My LWCO is a sensor in the boiler unit. I believe it's installed at the time of manufacture, so I assume it's where they want it. I'll send pics when I get a chance.



Boilerpro - Thanks for your advice on many parts of this site, Boilerpro. After reading a lot of your posts on venting radiators less instead of more, I think I've reduced some water hammer I had early in the cycle by following your advice.  Let's hope it stays that way. My LWCO only cuts out the system when the water drops too low.  I don't think it has a foaming check system and if it does, I'm pretty sure that's not the problem. It only cuts out when it's low.  I do think I may have been filling the first radiators before the mains the way I had them vented earlier, but now that seems to be better. That still doesn't solve the cut-out problem, though.



Steve - Thanks for reading so closely. Yeah, I tripled the main vents based on this site's recommendations. It seems to clear the pipes of air very quickly.  How do I check whether the hartford loop is clogged (yes I do have one). Will send pictures once I have a minute.



Charles - Yeah, see my comments to Boilerpro. I turned the vari-vents down all the way except for two bigger radiators in colder rooms. The house heats up more slowly, but early-middle cycle water hammer seems to be down and the house seems to be heating more evenly.   Pennco 1604 is the boiler. See above for link to manual.



Thanks a ton to all of you. I really appreciate getting some sound advice. I know how hard it must be to do this from far, which is why I didn't want to start asking questions until I had read a ton on this. I'm at a loss and getting inconsistent and seemingly off-base answers from the pros I've had look at this, so it's good to hear some sense that might lead me to an answer.  I've been battling/learning for 2 years now and I have to say that aside from the fact that it drives me nuts, this steam stuff is pretty amazing.

Charlie from wmass

Slower vents on the radiators,

delay the water feeder, and flush out the returns. A photo of your near boiler piping will speak volumes. I like the ecr international boilers as a whole Utica is the name we use from them.

Charlie from wmass

The Gorton #2 vents

What size of pipe are they on? 3/4" or 1/2"? Also what is the length and size of your mains? Have you confirmed proper pitch of all the steam lines? I am betting on clogged returns though.

nicholas bonham-carter

clogged returns?

if the auto fill has the water inlet valve turned off, how long does it take for the waterline to return to normal after steaming and subsequent cut-off?

the horizontal return which could hide water, would be one whose height would be in the area where the water rises in the returns because of boiler pressure. when the rising water encounters a horizontal pipe, it has to fill it before the waterline can reach its new level governed by the boiler pressure. difficult to explain, but i will keep going. when pressure rises in the boiler, the boiler waterline drops enough so that the level in the wet returns rises up 1.75 in. per ounce of pressure. usually it does not take too much water to raise the return level, unless...........there is a horizontal pipe just above the waterline. the rising pressure tries to raise the return level, but has to fill this horizontal first, and that can take a bit of water away from the boiler. we had that problem, and only after much head-scratching nailed the source of the problem. a couple of 6 ft. sections of 2 in. pipe can hold enough water to drop the lwco out. after steaming, the water came back quickly.

turn off the auto fill and see how long the water takes to return.--nbc

crash2009

Thanks for the manual.

 I looked at it last night.  I am unable to open pdf's from this workstation, but I think your manual  (check to make sure) said your waterline in the sight glass should be 24" from the floor.  I don't remember who said it, but I remember reading here on the wall that some boilers, require an exact waterline. not 23 1/2", not 24 1/2", but exactly what it says in the manual 24".  That is what I meant when I asked if your boiler was "picky" about its waterline.

So, I am suggesting that you get the waterline exactly correct if it is not all-ready.  Also mark the correct waterline, on the sightglass with something, fingernail polish, felt marker, etc.

Keep a tape measure handy to measure the ups and downs, and write it down in a log book.  After a few cycles a pattern will become evident.  Another reason to start the log book is if you ever have the same problem again, you will know exactly what to do.  Assuming you write down the solution once you find it.