fluctuating water and possible overheating in outdoor Central wood boiler

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Old 11-01-13, 06:22 PM
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fluctuating water and possible overheating in outdoor Central wood boiler

Ok this is really weird. I've had this Central Boiler for years and this has never happened.
Over the last few weeks I've noticed wild fluctuations in water level as measured by the little valve intended for that purpose. You open the valve, water fills a plastic tube, and you read the level. I just filled the tank the other day. It was low, which is unusual, so I checked for leaks and found none. So I filled it, and it stayed at the normal level for several days. One day I noticed the vent cap was ajar, and it was steaming as if overheating. I put the cap back on and it simmered down. Then the other night when I checked it the water level overflowed the top of the check tube, as if it water had somehow been added! Next day it was normal level again. I haven't noticed any more steaming. Today, water level had dropped well below normal, and the vent cap was ajar, as if it had been popped off by overheating again, but it was not steaming. My temperature gauge is broken but it is easy to HEAR when it is overheating and it wasn't, except for the one time I saw it steaming.

I just replaced my pump cartridge last week because the pump was making a little noise. I wonder if the pump motor may be going bad? As far as I can tell the damper is closing so that shouldnt be causing overheating. Overheating could be causing the water to steam off and drop the level, but what could cause the water level to rise, other than maybe a bad pump?
 
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Old 11-02-13, 08:37 AM
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You're right Wayne, this IS weird!

what could cause the water level to rise, other than maybe a bad pump?
A bad pump can't add water to a boiler...

If your pump isn't moving any water it is possible that is what causes the overheating. Even with the damper closed, it's possible that with no water movement it can still overheat.

Are you getting hot water into the home at all times?

You might have a couple of problems...

Maybe your fill valve is leaking and flooding the boiler... AND your pump isn't always pumping?
 
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Old 11-02-13, 10:16 AM
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I think I may have figured it out, or at least part of it, thanks in part to my friendly dealer. I have a domestic hot water heat exchanger at my hot water tank. The only way for water to get in to the system is if that leaks and exchanges water instead of just heat. But since its 100% copper except for the soldered seams, that is rather unlikely under normal circumstances.

But I found a substantial air leak (rust) in the cleanout port of my stove. When I closed that off temporarily with duct tape, smoke during the damper closed cycle was immediately reduced to just a few wisps. What was probably happening is that when the boiler reached temp and the damper closed, that leak continued feeding enough air to push it to the boiling point and cause steaming and maybe spillout, lowering the water level. I'm guessing (and it is just a guess) that when it was overheating, that might have opened up a small temporary leak in a seam of the heat exchanger, and water leaked from my pressurized water into the boiler line. Then when it cooled down, the leak stopped. That's my best guess anyway...if you have a better one let me know
 
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Old 11-02-13, 03:00 PM
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I dunno Wayne... I might buy the part about the air leak, but the part about the 'temporary leak' is kind of a stretch.

Keep us posted what you find, and double check that the valve you are using to fill the boiler is really shutting off 100%.
 
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Old 11-02-13, 03:16 PM
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yea, my dealer didn't like my temporary heat exchanger leak theory either. Crap. The other, uglier and unavoidable possibility is that the heat exchanger just plain old leaks, and I don't want to think that because it was a MAJOR PIA to install just a month ago (because of where the water heater is located) and I DO NOT want to do that again! Ever! But there is no fill valve to leak; you fill the boiler with a hose so the exchanger is the only place it can come from.

I'm going to watch it for a few days. Now that I think I've solved the water drop problem, it should be very obvious if it keeps rising.
 
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Old 11-02-13, 05:40 PM
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Is this a 'side-arm heat exchanger' ? If so, isn't it a pipe inside a pipe? I doubt if there are any seams inside of it.
 
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Old 11-02-13, 09:13 PM
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It is indeed a side arm. I think it is a coiled "pipe" inside a copper jacket. I used it for a couple of years, then it sat for a number of years, then I reinstalled it a month ago. None of the other copper pipes laying around my garage have sprouted holes, so there must be some corrosable innards in that coil somewhere.
 
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Old 11-03-13, 07:41 PM
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Both theories were wrong. I was out by the stove tonight when I heard the damper solenoid turn off. But the damper door didn't close. Thats why it was/is overheating, though its weird it never happens when I'm around except that once. I'm thinking it overheats when I'm sleeping because I put more wood in there late at night.

I just lubed the damper and solenoid a few weeks ago too.
 
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Old 11-09-13, 09:24 AM
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Well I think the great mystery is solved and it was far less complex than it seemed. Draft door solenoid was only functioning some of the time, causing overheat and spill over; when the water was rising from overheating, it looked like water was being added to the system. Pretty damn simple. New solenoid; no more problems (so far).
 
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Old 11-09-13, 10:38 AM
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Interesting...

Yes, heat water from say 70 to 180 and it's volume increases almost 4%, so I guess I can see how that would look like water was added to the system if you were heating to 212 and steaming...

How many gallons of water in that boiler? 150? so say heating to 212 is maybe 6% volume increase, that's the same as adding almost 10 gallons extra water to the system. Is that about what you guesstimate you were seeing on the level gauge?
 
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Old 11-09-13, 10:57 AM
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I guestimated by how long the hose ran when refilling that I lost about 15-20 gallons each time, but that was purely a guess. It may have been more, but certainly not less. The boiler holds 180. But we're only talking about expanding from 160 or so to 200+ (I'm at about 800' ASL) . Except for right after adding water the boiler water shouldn't have dropped below about 160, and even then I doubt it dropped lower than 140 or so. Since my temp gauge is busted I don't know exact numbers. But I've had 48 hours without a loose vent cap or change in water level since I changed the solenoid....
 
 

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