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Steam Boiler Overfilling, water hammer - LWCO?

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I recently had a professional HVAC company come out to service my gas steam boiler. The return lines near the unit were completely clogged, so the company took apart all return pipes near the boiler and cleaned them out. Afterwards, they took apart, cleaned and reassembled the Low Water Cutoff unit which "was very dirty" and installed new gaskets.

Before this service, water level was exactly half way up the sight glass. I know this as the same company comes out every year to perform yearly maintenance and I clearly remember the water level being 100% correct. After the LWCO was serviced, the water level is high and appears to be near the top of the sight glass. When the unit is on and operating normally, the water level fluctuates around half way up the sight glass, but will eventually return to an overfilled state when idle.

To add to the problem above, water hammer can be heard throughout the system during start up, but will eventually stop after the unit warms up. Again, this water hammer was not present prior to the service.

My questions are:

1.) Can an overfilled boiler cause water hammer?
2.) Can the LWCO be adjusted to allow the water level to be exactly half way up the sight glass?

The company is suggesting the following. What are your thoughts?

1.) Verify pitch on all return piping to ensure 1/8" pitch per foot.
2.) Adjust firing rate of boiler to match existing load
3.) Use thermal imaging to test thermostatic return traps.


I need to start somewhere and I'd rather not spend thousands of dollars in service "guessing" on a solution.

Comments

  • nicholas bonham-carter
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    Is this one-pipe or two? Can you valve off the auto feed, and mark the water level on the gauge glass with clothes pegs, and observe any fluctuations of the level during a couple of days?
    Did they clean out the pigtail, and verify the pressure as being less than 1.5 psi? Is there an accurate low pressure gauge (0-3 psi), on the boiler.--NBC
  • superdave17
    superdave17 Member Posts: 6
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    1.) It is a two pipe system

    2.) I will valve off the auto feed today and monitor the water level for a couple of days. After I valve off the water, I assume I should drain the water so it is half way up the sight glass while the system is idle (not running)?

    3.) They did clean the pigtail on pressuretrol. (That's what the invoice indicated).

    4.) The pressure gauge on the system is broken. I need to have it replaced.

    Prior to cleaning of the return pipes, a technician changed the pressure of the system from 1.5 PSI to .5 PSI. Before this change, there was no water hammer. Should I change it back to its original 1.5 PSI setting?

    Also, one of the radiator units was removed over the summer and the suppler/return lines were capped. Could it be possible that there is condensation building up in these two lines that are not being used anymore and causing water hammer? I was advised that this would not make a difference (which is why I had them remove it).
  • Abracadabra
    Abracadabra Member Posts: 1,948
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    Was any new piping installed?
  • superdave17
    superdave17 Member Posts: 6
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    No new piping was installed. However, they discussed having all return piping cleaned that hangs near the ceiling. This would be quite an undertaking as the pipes are original and close to 100 years old.

    They cleaned all return pipes near the boiler, so only about 4 feet worth. There is close to 50 feet of return piping total that still can be cleaned. I'm even considering having the piping replaced.

    I have attached some pictures of the boiler model and pressure settings. I also attached a picture of the sight glass being almost full while the boiler is running.






  • Fred
    Fred Member Posts: 8,542
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    Judging from the looks of that sight glass, I am not sure they did an actual maintenance on that boiler. They should have taken that glass off and cleaned it. Anyway, the setting on the front of the Pressuretrol is correct. Take the cover off of the Pressuretrol and inside is a white wheel that should be set at "1", facing the front of the unit.
    With the water level that high, you don't have enough room in that boiler to make steam. That is likely causing some of the hammer. As has been said, shut down the auto water feeder, lower the water in the boiler and run it and see if that resolves the noise problem. It is possible the auto water feeder is defective, allowing water to seep past the solenoid valve and over filling the boiler. Did they add any chemicals to the boiler? It is also very possible that they added some type of cleaner to the boiler and that is making the water level unstable enough that the LWCO is sending a signal to the auto feeder to add water and then the boiler is over-filled when idle. If they added a chemical, drain the boiler, and refill it to get the chemicals out.
    Also, Mains and dry returns, up near the basement ceiling don't need to be "cleaned" and they don't need to be replaced unless they leak, which is rare.
    MilanD
  • Abracadabra
    Abracadabra Member Posts: 1,948
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    No new piping was installed. However, they discussed having all return piping cleaned that hangs near the ceiling. This would be quite an undertaking as the pipes are original and close to 100 years old.

    If they are talking about "cleaning" the dry returns which are up above the waterline, find a different contractor. They are idiots. I have never found a dry return that needed any kind of "cleaning" even after over 100 years. Wet returns below the waterline are another story.

    I'm guessing either the feeder is leaking or your manual fill valve is leaking.

    I would also reccomend adding a 0-3 psi gauge to ensure the pressuretrol is doing what it's supposed to and shutting off when you think it is. When they are set that low, weird things can happen and they aren't reliable that low.

    MilanD
  • superdave17
    superdave17 Member Posts: 6
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    To follow up:

    1.) Yes, the Pressuretrol is set to "1" inside of the unit

    2.) After shutting off the water supply and draining the unit so water level is half way up the sight glass, loud water hammer is no longer present! There are soft knocks every so often which I assume are normal (very faint knocking and far between).

    3.) From what I understand, the servicing company did not add any chemicals to the system.

    4.) I believe the return pipes near the ceiling are wet returns. Two months ago the main wet return near the boiler became clogged and water began pouring out of the vent near the ceiling. I know wet returns are to be below the water line but the piping system is close to 100 years old so it may not be up to modern standards. I can provide pictures if it helps.


    With the water supply off, the system functions normally. Water level did decline about an 1/8th of an inch on the sight glass over 3 days - I assume that is normal.

    Should I have the automatic water feeder replaced first? Is there any way to test if it's leaking?

    Is it possible that the LWCO was rebuilt incorrectly causing false signals to be sent to the water feeder to add more water and overfilling the boiler?


    I am beyond thankful for your advice and recommendations. You have helped me tremendously and saved me thousands of dollars. The company quoted me $1,500 per day in troubleshooting.
  • MilanD
    MilanD Member Posts: 1,160
    edited February 2017
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    Fyi: any pipes below water line of the boiler are referred to as "wet returns". Fact your line was clogged and water backed up and came out of the main vent still makes those retuns above the water line "dry returns". A little cinfusing terminology.

    Lwco feeding water would also cut out the burners first. I'd suppose you should watch if your burners are cutting out when water level drops during notmal op. If that's the case lwco is probably fine. You can delay the fill by a few minutes with different toggle/jumper settings inside the autofeeder, to give a few minutes for the condensate to return.

    I'd then turn the boiler off, open the valve on the autofeeder for a few hours on the normal water level in the boiler, mark the water level and then see if it rises without the system being on. This would signify the feeder is bad.
  • nicholas bonham-carter
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    Cleaning the sight glass is pretty easy, and being able to see clearly the level is a real plus. The fact that they did not clean it during the maintenance shows them to be unknowlegeble.
    Your first priority should be the low pressure gauge. That will tell you if the pressuretrol is functioning properly, and if you have enough main venting.
    I suspect the pressure is getting high enough to push much of the water out of the boiler backwards into the wet returns, causing the water level to go low enough to trigger the auto feed. A clean sight glass will make this monitoring easier.--NBC
  • Chris_L
    Chris_L Member Posts: 336
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    To follow up:

    Is it possible that the LWCO was rebuilt incorrectly causing false signals to be sent to the water feeder to add more water and overfilling the boiler?

    I believe it is. There are actually two switches in your LWCO, one to shut the boiler off on low water, one to activate the water feeder. They may have got them backwards when they put it back together.

    The pros here can tell you what effect that would have on the water level better than I can.

  • Fred
    Fred Member Posts: 8,542
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    Any returns above the Boiler's water line is a dry return. Any below the boiler's water line is a wet return.
    I', not sure if the wet return was ever clogged or if the water feeder simply failed and added enough water to back it up and out of the vents. The water feeder needs to be serviced or replaced. It should be left off until that problem is fixed. During that time, you need to check the water level in the boiler and add water manually when it gets low.
    If the LWCO were wired incorrectly, sa as to call for water, the boiler would have shut itself down waiting for water to be added. The problem is the water feeder. A relatively common problem.
    You need to walk your basement and check where the hammering/noise is coming from. If it is truely hammer, it will be loud and indicate a pipe is either sagging and holding water or a pipe is pitched the wrong way (or has no pitch) and holding water. When steam hits that water it will hammer. It may well be expansion/contraction noise where a pipe is rubbing against a wood floor or other structure. In any case find the source of the noise. Steam systems are virtually silent systems.
  • Abracadabra
    Abracadabra Member Posts: 1,948
    edited February 2017
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    MilanD said:


    Lwco feeding water would also cut out the burners first.

    No. MM67 (which it looks like from pictures) will activate feeder first when level drops. If level continues to drop further, then it'll kill burner. Assuming it's wired correctly.

    Haven't seen a picture of the feeder, so don't know if it's a MM101 or something else. But water can leak past the feeder. 101 has a replacement cartridge to repair leaks. Strainer is usually replaced at the same time.
  • superdave17
    superdave17 Member Posts: 6
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    Yes, it's a MM101-A-24V water feeder. I have a quote of $700 to replace it.

    Should I try replacing the cartridge and strainer first? Do you have a link to a site that I can buy both? I tried searching online with no luck.
  • Fred
    Fred Member Posts: 8,542
    edited March 2017
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    Yes, it's a MM101-A-24V water feeder. I have a quote of $700 to replace it.

    Should I try replacing the cartridge and strainer first? Do you have a link to a site that I can buy both? I tried searching online with no luck.

    I have not had good luck replacing the cartridge/strained. The solenoidusually also tends to weaken/fail and allow water to seep by. I would replace the entire unit. Here they are at about half the cost of your estimate if you are willing to install it yourself. Be sure to order the 120V or 24V, depending on what you need:
    http://www.supplyhouse.com/sh/control/search/~SEARCH_STRING=McDonnell Miller 101A
  • Abracadabra
    Abracadabra Member Posts: 1,948
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    I have never had issues with replacing the cartridge and strainer on a MM feeder and not holding when properly replaced. If the inlet and outlet ports on the valve assembly do not have the hex shape and are round you need to replace the entire assembly, you can't just replace the innards.
  • Fred
    Fred Member Posts: 8,542
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    I have never had issues with replacing the cartridge and strainer on a MM feeder and not holding when properly replaced. If the inlet and outlet ports on the valve assembly do not have the hex shape and are round you need to replace the entire assembly, you can't just replace the innards.

    Yes, my valve assembly was round.
  • Lordofthering
    Lordofthering Member Posts: 14
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    Replace your water feeder. Until then turn of your automatic water feeder and do manual feed. All your problem should be solved. Keep water level around half or little more of sire glass
  • Bob Gagnon plumbing and heating
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    Lord is right, manual feed is best, it'll alert you to any leaks in the system, I would consider changing out 100 year old wet returns.
    Thanks, Bob Gagnon
    To learn more about this professional, click here to visit their ad in Find A Contractor.
    MilanD
  • superdave17
    superdave17 Member Posts: 6
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    I have the company coming back tomorrow to install a brand new water feeder and also a new pressure gauge.

    I will follow up in this thread after a few days, after monitoring the water level.
  • Grallert
    Grallert Member Posts: 646
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    Correct me if I missed it but it doesn't sound like your boiler was over filling? But that it was over filled. In other words the water level in the glass did not continue to climb? I'll read through again but it seems like the service crew simply over filled the boiler after the wet return work was done, causing the hammer which you resolved by bring the water level back to its normal. If the above is true you might not need a new feeder. If you are getting one i would suggest getting one with a meter on it.
    Miss Hall's School service mechanic, greenhouse manager,teacher and dog walker
    MilanD
  • BobC
    BobC Member Posts: 5,479
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    Kick this up to that world renowned expert in fluids for the definitive answer - Gen Jack D Ripper

    https://www.youtube.com/watch?v=N1KvgtEnABY

    Bob
    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge