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Condensate pump + two LWCOs + water feeder nightmare

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Guys, I'm losing my mind here. I've made lots of progress this year on things like steam traps, venting, pipe and radiator pitch, insulation and eliminating leaks. My system runs perfectly 99% of the time, but I have a recurring control failure that happens about once a month and it's driving me nuts. Here's the situation:

1. There's a float-operated condensate pump on the system. If the water level drops below the LWCO cutoff point, a relay shuts off power to this pump, so the water will never get back to the boiler. The tank (Hoffman WC8) seems to be somewhat oversized for my system, but I've used up all of my steam work budget and then some for the year so it will have to stay for now. Adjusting the float to minimum travel has made it work reasonably well most of the time.

2. There are two LWCO's: One electronic probe type cutoff that will shut the boiler down, and the older float LWCO that only controls the automatic water feeder. The cutout point of the electronic LWCO is above the level where the float turns on the water feeder. So, if boiler shuts off on low water between these two points, I get a shut down boiler and no water coming in to allow the system to turn back on. Since the power to the condensate pump has now been cut off, all of the water in the system will collect in the receiver tank and the returns behind it, waiting for me to come downstairs to add that little bit of water that will make the system come on again.

3. The boiler is at least 20 years old and header and equalizer are piped in copper. However, the size and configuration of the header and equalizer meet Weil McLain specs and it produces reasonably dry steam. Since return is from a condensate pump, there is no Hartford loop. I'd love to turn this back into a gravity system, but the significant changes to all of the returns, the location of the venting plus the need for a new header and equalizer means I'm not going to do it until the day this old boiler needs to be replaced. Beyond that, I have a large buried dry return that would be turned into a wet return in a gravity system. I don't want to turn that into a wet return without replacing the old pipe. Not in the budget right now.

So anyway, like I said, about once a month I have this annoying shutdown issue and I'd like to eliminate it. I monitor the system for water losses, and it doesn't lose water. Since the water feeder is essentially non-functional right now, I just leave it valved off. The only time I add water is when this shutdown issue happens, and when everything pumps back from the condensate receiver, I can see that there hasn't been any system water lost in the event.

Here's my thoughts about my options:

1. Remove the relay from the condensate pump's power supply, so the pump can still run if the boiler is off on low water.
2. Connect water feeder to the electronic LWCO instead of the float LWCO. I'd do this, but the manual doesn't tell me how to wire it.
3. Just remove the electronic LWCO from the system entirely, as there's nothing wrong with the float one. Return the burner cutoff function to the float LWCO. That way the water feeder and the cutoff will operate on the same water line again.

Thoughts? Anything I'm missing?

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 23,650
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    Can you rewire this puppy so that you the condensate return pump acts more like a boiler feed pump? I dislike condensate return pumps on principle, particularly when you have a fairly large tank.

    You may have to rejigger some levels. I would set it up so that you had a low water sensor (let's not call it a cutoff, eh?) which turned on the condensate return pump -- which we will now term the boiler feed pump. Then I would have the float in the condensate tank set up so that if the condensate tank got really low it activated the "automatic" water feed. Then I would have a true low water cutoff to shut off the boiler if things went west and the boiler water level really truly did get low...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Waterbury Steam
    Waterbury Steam Member Posts: 58
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    That leads me to the question--is it possible to do this with the current Hoffman pump and McDonnell Miller LWCOs? I've tried to find documentation on converting the condensate pump to a boiler feed setup and I can't find anything about how to do it.
  • Jamie Hall
    Jamie Hall Member Posts: 23,650
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    The only difference between a boiler feed pump and a condensate return pump (in a home heating situation!) is what controls it. The boiler feed pump is controlled by the water level in the boiler, while the condensate return pump is controlled by the water level in the condensate receiver. It's more a matter of which switch controls what... than anything particularly exotic.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Waterbury Steam
    Waterbury Steam Member Posts: 58
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    I'll consider that as a long term solution--looks like that will involve another LWCO/pump controller change and the addition of a Hoffman control box for the pump. These are the kinds of expenses I'm hoping to avoid right now, and would have to balance against just going for new near boiler piping and gravity return.
  • Jamie Hall
    Jamie Hall Member Posts: 23,650
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    Indeed. New near boiler piping and gravity return is a much better idea!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Waterbury Steam
    Waterbury Steam Member Posts: 58
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    Yeah, as an engineer I hate band-aids. But, money is money and I just need one for this season to prevent this one little control glitch that might happen once every 200-300 cycles. I'm thinking that removing that stupid relay is probably going to get me what I want. I have no idea why the installer thought years ago that I wouldn't want the condensate pump to start when there's low water in the boiler.
  • Jamie Hall
    Jamie Hall Member Posts: 23,650
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    Some things are just plain mysteries... go for it.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • sreja
    sreja Member Posts: 175
    edited November 2014
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    I'm not a pro, so follow the advice of the pros first, but my 2 cents:

    We have a condensate return tank on our boiler as well.

    You say your condensate return tank pump gets shut off when the boiler LWCO triggers? That sounds completely wrong to me.

    Part of the reason this sounds so wrong is that when the condensate tank pump triggers, it can cause the boiling water level in the boiler to collapse, dropping the water. So it wouldn't be surprising to have the LWCO cut off frequently when the condenstate pump runs.

    I can't think of any good reason that the LWCO should be wired to affect the condensate tank pump.

    In our case, the condensate tank pump runs whenever it accumulates a significant amount of water, and that works just fine.
  • Waterbury Steam
    Waterbury Steam Member Posts: 58
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    Yes, that's correct. If the water level gets too low in the boiler, the LWCO will trigger a relay that prevents the pump from starting and all of the condensate in the system will back up in the condensate tank.

    I've never seen the pump cause the LWCO to trip while it's returning water--it just reduces the steam pressure for a bit but never causes any surging, hammering or anything bad in the boiler.