LWC water level drops below furnace water level

DavidM

This problem stumps me and the servicer's steam professional. It is certainly hurting boiler efficiency, and is a big nuisance. I have a large old house (in the Pacific Northwest) with a gravity fed system using a probably 55 year old oil GE boiler. See photos. Mains are huge and returns also ample. See photos attached. House has 3 floors above basement. Feeds to radiators are piped vertically from a 50-yard, down-sloaping loop in the basement (leaving to left on 1st photo) which then loops back to return. A nearby riser comes off on right on photo. Various returns come back and join near floor. Then join with (if my terminology is correct) Hartford loop above boiler waterline to feed boiler. Water feed is near entrance to boiler at bottom. The low pressure cutoff - feeder is piped to Hartford Loop at the levels which correspond to the bottom feeder tube of sligh-glass and level about two inches above top of sight glass. The air vent for the system sits high above the furnace on the returns.



Some of the radiators are correctly piped. Others, added later during an addition, are baseboard heaters. The house has tilted a bit over the years, and these baseboard heaters have some knocking, but not too bad. Condensate takes a long time to return to the boiler. There are no traps in the system. The boiler pressure is running up to as high as 2.5 psi. I believe it used to operate at more like 0.5 or 1 psi (but am not sure).



When the boiler is not in operation and the low-pressure float chamber has been blown out, the levels of operation of the feed, and the switch on and off are precisely what is specified in the directions for the M&M 47-2. (I have cleaned the M&M 47-2 out, and can't find anything wrong with it. When the boiler operates, the level in the sight glass raises slightly; and there is about 1/2 inch of fluctuation. However, the level in the float chamber of the LPC apparently falls. So much so that in order to keep the boiler going one must fill 4 or 5 inches above the normal cut-off point. -- which is too high. When you open the blow-out valve of the LPC, water comes out followed by steam. After about 10 seconds of purging, the LPC works (temporarily) at the correct levels. Obviously the system has pushed the water level down in the LPC.



I cannot, the professional cannot, figure out why the pressures don't equalize to keep water at the correct level. The equalization piping seems to be open: when water flows from the furnace after the LPC is emptied, it flows about as fast as one would expect, given the slight difference in water height of a few inches between the LPC inlet and the furnace. Assuming the boiler water is in the middle of the sight glass, It would take about 10 seconds to turn the boiler on. I can't think of any reason why the water height in the Hartford Loop would not be about the same as in the furnace.



One other piece of information: I believe the above problem existed to some extent last year, but it is now worse. Radiators were detached, cleaned and reattached two years ago.

jpf321

a few things ..

1) did it ever work properly?

2) the Tee for the hartford loop is supposed to be BELOW the Normal Water Line (NWL), the Tee for a Gifford loop is supposed to be above (but I don't want to confuse you, please read article in #8)

3) The abbreviation of LPC doesn't compute, do you mean LWCO (Low Water Cut-Off)

4) You mention that you think you are now running at a higher pressure, that higher pressure could be affecting this. Did anything change? did you play with your venting? is all your venting checked and cleared? or are some vents plugged and not blowing clear?

5) Water rises 28" for ever 1psi so that extra 1psi that you think is different now pushed water 28" in some direction?

6) Did you check your pressure-trol? What is it set at? Should be cranked down low on both outside gauges and inside thumbwheel turned to #1.

7) I'm not sure that it's common to pipe your LWCO into your Hartford/Return piping since I think they fluctuate too much, that's why I ask if it ever worked?

8) Have a look at this article which describes what happens to water level and pressure  in a Hartford/Gifford Loop, perhaps it will some idea flowing in your head: http://is.gd/geAtg

9) Is your LWCO piped into the Equalizer coming from the header/main? It looks like it could be. since your LWCO is connected to your piping rather than your boiler/sight-glass, you may be pushing the water in that piping below the waterline. Pressure starts at the boiler and pushes outward.

10) Is this a 1-pipe or 2-pipe system? Because you say there are no traps, I assume 1-pipe?

11) What is the vertical height in inches from your NWL (boiler at rest and pressure = 0) and the lowest end of the overhead mains? This is called Dimension A.



That's all I can think of for the moment. I wonder if you can annotate your pictures a bit with NWL markings, I see there is a mark on the boiler, but an annotation overlaid might be very helpful. Or at least a picture taking straight on and level with the NWL mark, so the affect of photo angles is dimished. I use Picasa (http://picasa.google.com/) to annotate my pictures.



Looking forward to more feedback.

jpf321

i have a feeling...

that your Dimension A is too short, and therefore your boiler is pushing outward and the water is creeping into your horizontal mains instead of stacking vertically and exerting downward pressure. (28" = 1psi) You need that stacking to push water back into the boiler and overcome the pressure exerted outward at the boiler. OR you need to decrease boiler pressure so that the stacking is enough to overcome the outward boiler pressure.



If you don't have enough stacking at the end of your main, then your water in your boiler side return pipes will be pushed (by the boiler) below the piping of the LWCO, thereby making it "DRY" or empty rather than "WET" or under-water-line.

jpf321

check valve...

i also notice that you have a check valve above your paint roller tray

.. that may have something to do with the problem as well. is there an

arrow on the check valve .. which way is it pointing?

jpf321

does blowdown shutdown?

when you blowdown the LWCO and you say that you see steam coming out, does your boiler shut-off like it's supposed to ..



are both of the valves on your sight-glass fully open?

DavidM

Answers to questions raised.

The boiler has apparently been installed since the mid-1950s (if memory serves) and has worked over the years. My wife has lived here 19 years and it always worked during that time. I have lived here 7 years, and last year was the first with problems. It hasn't been repiped in 19 years, though the pipe insulation was changed at the basement level 2 years ago...and -- perhaps relevant -- the returns may have been additionally insulated.



The input for the returns to the loop is just above the line on the LWCO.



I checked my main vent this morning and it was clear.



I am wondering, as you, whether the extra PSI, if it exists, affects the system, but I don't see how.



The high pressure control is set at 2psi and the differential wheel at 1. If I set it lower, I will have to do frequent manual restarts.



The system is 2 pipe. The distance between the ceilings and the floor, as well as the major slant in the returns and the large pipe sizings allow this to work without knocking.



The distance from the mid-line on the sight glass, which I assume is the preferred normal water line to the bottom of the header is about 30 inches. The cut off level is about one-half inch above the bottom of the sight glass and the fill level is 1 1/2 inch. above that.



I can annotate my photos, but will not get to it this afternoon. Thanks for your help so far!

DavidM

More answers to questions

I asked the steam professional about the valve above the paint tray and he said it was merely a shutoff valve, and that it was open.



Both valves on the sight glass are open and working correctly.



With the furnace off, of course only water comes out, and the shutoff works correctly.



With the furnace hot, overfilled and working, or normally filled but with a premature cutoff, that is when you get the steam...and yes, it cuts off in the first case because water comes out first.



I am trying to understand your comments about the dry returns.

Steamhead

Not the right place for that feeder

the 47-2 was designed to be hooked up to the sight glass fittings. Only there can it accurately measure the water level in the boiler.



There may be a built-in LWCO on that boiler somewhere, most likely a M&M 69 series unit. If so, a feeder like a Hydrolevel VXT could be wired to it. If the built-in unit has failed, and it's a 69 series, it can be repaired.

DavidM

Problem may be solved

I'll post a definitive answer after more experience. First, an error above...the high pressure cut-off does not require a manual restart.



In reply to steamhead, about the 47-2 supposed to be on the sight glass fittings, apparently so from the installation instructions, but it has performed satisfactorily for years.



I believe the problem is solved, though I still don't know why exactly. Based upon the posts of jpf321, without understanding them completely, it seems that the A distance is related to the operating pressure. If so, if the operating pressure exceeds 1/2 psi or 1 psi, steam rather than water could get into the LWCO. There would be residual water in the LWCO below the level of the inlet pipe. I have just tested the system filled to the proper level for about an hour in which the pressure did not even reach 1/2 psi, and the LWCO is not calling for water. If the HP cutoff functions at 1/2 or 1 psi, perhaps this condition will not occur. I know that the HPC has been set at a level above this for at least two years, but also had heard it should be set lower.



The pressure would rise only when the radiators are very hot and the steam doesn't condense. So another possibility is that steam is coming down the returns and that somehow that causes the valve to fail.



Another possibility, that I still need to test, is that the loop gets so hot that somehow steam gets into the valve. If so I would have to remove some of the new insulation on the loop.

jpf321

steam does not....

1) go into a pipe flled with water

2) go into a pipe filled with air



Did you look at the article in #8?



The check valve is the fitting with the "square nut" on the top, it doen not have a handle which you turn. It is directly above the right edge of your paint tray. It is brass.



Have a look at this drawing posted by jstar a while back:

http://www.heatinghelp.com/images/posts/2569/resize_A_dimension_operation.JPG

DavidM

Still LWCO water level drop -- under vacuum!

Thanks again, jpf321. I did read the article in #8 earlier. And thanks for the diagram. But won't the water run into the boiler when the system stops and the pressure equalizes? If so, does one have to start with a higher water level in the boiler? Which would be forced into the return as the system builds pressure (if there is no check valve)?



Have demounted and will replace pressure controller, as it does not function accurately. So no more tests until Monday. But have run some this afternoon.



New info: when the thermostatt shuts the boiler off after running at 2 psi, a vacuum of 5 psi develops in about 1 minute, which took about five minutes to dissipate. (Later, from 1.5 psi, the vacuum reached 2.5 psi and took 2 minutes to dissipate.) The water level in the boiler sight glass dropped slightly. The LWCO, however, dropped much more and cut the furnace off. It came close to restoring itself in another 20 minutes, but still had a water level an inch too low. The only scenario I can imagine is if the water on the loop and the water in the LWCO flashed to steam. Would this be possible?





FYI, the valve is a check valve (why the professional said no beats me) and the arrow flow is towards the furnace (the loop and the LWCO) from the returns. Don't know if the valve still works.

nicholas bonham-carter

check valve in return

we had such a check valve wrongfully installed on the old american standard to provide a band-aid for over-pressure and bad returns. i am sure that it should not be there, if all is well with the piping. an uncontrolled waterline can put quite a bit of stress on the sections of the boiler, and shorten its life, as it did with our old boiler..--nbc

nicholas bonham-carter

hot flashes

when a vacuum develops, it can enable the water, at less than 212 deg, to flash to steam. this was part of the principle of the old vapor-vacuum steam systems.

if your vacuum persists for longer than a few seconds, it would indicate that your main-line venting is woefully inadequate, and that you are a prize customer of the gas company, as you are paying them lots of money to force the air out of the pipes, rather than let it out through proper vents!--nbc

jpf321

i wouldn't...

Trust the gauge in the picture. At thbe least go and get a new 0-30 better to get a 0-3 from gaugestore.com. are you basing the pressuretrol problems based on reading from that gauge? What probles are you having with the pressuretrol?



Open up the check valve and see if it has an operable flapper. You may even do a few tests with the flapper removed.



When was the last time you removed and cleaned/replaced any/all pigtails?



I have a feeling this is all a pressure issue. And getting a low pressure gauge on a new pigtail will certainly give you critical data that may now be lacking.

DavidM

reply to last posts

Thanks for the comments. How does one open a check valve? Unless the top opens by turning the square part, it would appear impossible...And to get it out would require repiping much of the system.



It may be that the pressuretrol is ok, but the simplest will be to replace it...and perhaps the gauge, as suggested, rather than spending more time.



Yes, the present system is less than efficient in many ways, but redoing it has not been recommended, as sizes of fittings, lenghts, etc., don't equal modern standards and piping is built deep into the walls. Fortunately our degree-days are many fewer than in snow country. There may be one spot where an additional vent could be installed, and I will look into it.



If hot flashes are the problem, it will hopefully be remedied when the pressure gets under better control -- because the vacuum was far less and shorter when the operating pressure was lower.

Charlie from wmass

In all seriousness

You need a new boiler. A decent contractor will have limited issues replacing that. No it is not easy and simple but pipe sizes are not an issue. If told otherwise find a different installer.

DavidM

Resolution of problem -- and thanks!

Following up on the flash theory, I figured that the water inlet to the LWCO was too slow, preventing sufficient water from enter the LWCO to replace any flashing to steam and to cool the LWCO down as well. I bit the bullet and dismounted the lower water feed piping yesterday, and despite the fact that water fed decently, found it nearly clogged along 6 inches of length, and greatly reduced elsewhere. Chances are the flash theory is correct!



Given that the LWCO needs to be repiped, and that I want a professional to do the piping (though I could do it...but thinking of a home-sale one day), I investigated the suggestion of mounting the 47-2 on the sight glass as ideally it should be, and this appears feasible and requires less repiping. Some adjustments will have to be made to the sheet metal casing around the furnace. There is some sort of disconnected GE controller on the furnace that I located near the low water line, but to test it would require refilling the furnace, and presumably it was disconnected for a reason. Using it would also require additional purchases. So I will stick with what I have.



Seeing the cost of a new Pressuretrol -- which appears to be exactly what I have already -- I have oiled the existing one, and now it seems to work just fine. I checked the pigtails and they were unblocked; they are now clean, as well.



Again thanks to everybody who aided in solving this! If there continues to be a problem, I'll start a new thread.

nicholas bonham-carter

installing a m-m lwco the right way

here is a pdf of the installation instructions for your lwco maybe the fittings are still around to put it on the sight-glass--nbc