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Water flashing to steam in a hot water heating system
Chevyjohn123
Member Posts: 7
Hi,
I'm a newbie here. I have a natural gas fired hot water boiler (1973 vintage Weil McClain) residential boiler and replaced circulator, relief valve and air vent last winter. More than once last winter and already a couple times this winter, I've been called and told that the relief valve had popped. I have gone and observed the unit while operating and the there are two things that puzzle me. First is the sound. It rumbles like a hot water heater that is scaled over but not quite as bad. Sounds like gentle rain hitting the roof. Second, the pressure gauge fluctuates like a steam boiler does when surging. After the third time observing this and trying to make sense of it, I am thinking that the water is flashing to steam. The pressure at rest is around 12-15 lbs. When running it bounces from about 12-20 but I've never observed it going any higher. When it lifts the relief valve (I can never get it to do it when I'm watching of course!) it settles down and runs ok for a while, but the pressure gauge still surges. The aquastat is set at 180.*
Any ideas what is happening and more importantly, how to remedy the problem? It's a medium sized home (approx 1800 sq ft) with 2 zones. Thanks.
I'm a newbie here. I have a natural gas fired hot water boiler (1973 vintage Weil McClain) residential boiler and replaced circulator, relief valve and air vent last winter. More than once last winter and already a couple times this winter, I've been called and told that the relief valve had popped. I have gone and observed the unit while operating and the there are two things that puzzle me. First is the sound. It rumbles like a hot water heater that is scaled over but not quite as bad. Sounds like gentle rain hitting the roof. Second, the pressure gauge fluctuates like a steam boiler does when surging. After the third time observing this and trying to make sense of it, I am thinking that the water is flashing to steam. The pressure at rest is around 12-15 lbs. When running it bounces from about 12-20 but I've never observed it going any higher. When it lifts the relief valve (I can never get it to do it when I'm watching of course!) it settles down and runs ok for a while, but the pressure gauge still surges. The aquastat is set at 180.*
Any ideas what is happening and more importantly, how to remedy the problem? It's a medium sized home (approx 1800 sq ft) with 2 zones. Thanks.
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Comments
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Aquastat
check the operating control aquastat. It's either set too high or may be defective. Is your pump on the supply pushing away from the expansion tank? If you're not "pumping away", it may explain the pressure differential. You also may have excessive scaling/sludge at the bottom of the boiler.0 -
Water flashing to steam in a hot water heating system
Hi, Thanks for the reply. The pump is on the return and the expansion tank is in a strange location. It is down low on the water feeder line. There is no air scoop on the system but an air bleeder is located in the attic and no air shows up there. I've flushed the boiler itself and it seems to be relatively clean water. I am planning on taking a closer look at the controller and possibly turning that setting down to say 160* and see if it still acts the way it has been. I am also going to install a larger expansion tank as one of the steps. I will try one thing at a time to try and pinpoint the issue.0 -
Gauges:
My old dead boss used to curse gauges up and down. He never trusted one. Two were better and if they didn't agree, the two that agreed over the third one was the one to trust.
Tridicator gauges are notoriously unreliable. Before going nuts, replace the gauge with a quality one. They often fail in the pressure side. When they read 12#, they are actually zero. If the boiler is at 200 degrees, and no pressure it may flash over. If there is enough pressure to stop steaming in the boiler, it might steam going out into the system, being pushed along by the circulator.
But on Weil-McLain 68 series boilers, I see the boiler water temperature controller go bad and over heat more than any other cause. Especially ones with a remote capillary tube in the tankless.Has anyone futzed with the wiring or the control settings? If you have a tankless water heater coil in the boiler and get your domestic hot water from it, 180 is a nice setting with the low/operating at 160. You can push to 190 and 170 and still be OK. If the controller is bad and over heating, it will overheat. If you have a Watts 1156 feed valve, pressure reducing valve that is painted a copper/bronze color, it is cast iron and probably not passing water properly. It may need to be replaced.
It isn't supposed to do this. Don't go overboard though. It is a simple problem with a simple fix.0 -
you are percilating
You have calcium deposits in the boiler, which causes hot spots in the boiler.
Only way to remove is with chemicals. Usually caused by excessive fresh water, and or over firing / low flow in the boiler0 -
Water flashing to steam in a hot water heating system
Thanks for the help. I am thinking the boiler has mineral deposits causing the problem as you stated Furnacefighter15. I replaced the expansion tank today just to satisfy my curiosity. I thought that maybe the diaphragm was weak from years of use, anyway, I also need to provide a bit more history. When I first worked on this system, the owner (my brother in law) wasn't even aware that there was a pump on the system. He has lived in the house for over 20 years! I would guess that the pump that was there hadn't run in many years so your assessment of low flow under firing could be right on the money. Now for the important question, how to flush the boiler. Can I use a muriatic acid and water mix or is there a specific product I should be looking for? Again, thanks for the help.0 -
Sludge and Pumps:
I doubt that your BIL lived in the house for 20 years and the circulator pump either didn't work or didn't work for some period. The house would have been cold. They either work or they don't.
Before you go off and pump things like Muriatic Acid into the system, run some water into a 5 gallon bucket. If you can see the bottom, it isn't all that bad. The only way you could get enough water passing into the boiler and system is if you had a major leak or a bad case of leakitis. Supply houses sell "Boiler Conditioner" but they are more for steam systems and my old auto shop teacher always used to say that you can't buy a mechanic in a can. Many years in the trades haven't ever proven him wrong. I usually find that problems as you describe are more sinister and simple. I've built 4 houses for myself. I've installed an unremembered amount of FHW systems. I've worked on even more. I've never seen a system with all these problems that everyone describes and are all in a dither about solving anticipated problems.
I've never encountered a problem as you describe that wasn't resolved by some adjustment. And it didn't include a major re-pipe job. Hydronic FHW is the most forgiving heat that you can install and work on. I've worked on things that by the rules, shouldn't work. But they did. Some could use a fine tune like splitting zones. But never something that flat out didn't work.
If you can purge air from your system, you can purge water from the system. But if you don't have pristine water, you will just add the junk back in. If the water is really nasty, figure out why first. Save yourself some aggravation.0 -
Water flashing to steam in a hot water heating system
Thanks one more time. The water in the system is quite nasty and I've flushed some of the gunk out. I am still thinking that there is a mineral deposit in the bottom of the boiler as it makes the rumbling, bacon sizzling sound when the temp gets to around 160* and keeps doing it until the burner shuts down. I do have access to a commercial delimer that is used to delime hot water coil type heaters. I'm thinking I can shut down the boiler let it cool, drain and flush out the gunk out then run the delimer and see if it improves. The water resembles water from a steam boiler. All things seem to point to water that is flashing to steam at some point in the heat cycle.0 -
De-liming:
I doubt seriously that your problem is lime or deposits from hard water unless you have had a situation where you were consistently adding very "hard" water containing a very high concentration of total dissolved solids (TDS). Iron is not a TDS once it comes out of suspension. You should be able to flush out any stuff that is in the bottom of the boiler.
You need to think like water flow. You need to feed the boiler from the supply and drain out the return. If the boiler is fed from the bottom of the boiler, and you open the drain, the water will by-pass the whole boiler to go out the drain. You need to make the water go where it doesn't want to go. If you use chemicals, you may just put the iron back into suspension.
If "I" were doing it, I would probably try using my air compressor and blow air into the system while draining the boiler. Cycling by filling and draining. It is my experience that you can do a decent job of cleaning a system by draining it with compressed air and refilling it with water. Then draining it with the air pressure and filling it repeatedly.
I do this often when I drain and winterize houses that had the heating systems installed by musicians and/or psychologists. Ones who think that pitch is a musical term and a "low point (with drain) is a bad time in a life. And now, no way to get all the water out of the series looped baseboard.
Before you get too nuts on this though, check the PH of the water. $100,00+ will buy you a PH test meter. I find that a pool PH test kit works well and is a lot cheaper. You can get one at the big orange box in the pool supply section or a pool supply house. 5 drops of water and a drop of regent will instantly give you a result. Yellow and you have acidic water that is not good. Shades of green mean the PH is high. Check the water in your house. If it is yellow, whenever you add water, you are adding acidity. Filling the system with air will oxidize the solid iron on the boiler and pipes and make it easier for the water to wash it off. It is often in the form of a slime that only the turbulence of the air will loosen.
That's my experience. Some may think I am full of schitt but when I purge a system or air in the Spring, the purged water usually looks like crud at first. A few years of doing this, the water gets cleaner if the make up water isn't acidic.
Do you have a tankless coil in the boiler? The noise may be coming from a seriously limed up coil.0 -
Water flashing to steam in a hot water heating system
Hello again Icesailor,
The water is city water but I will check Ph and hardness. I did change the expansion tank, didn't make much difference. The water feeder is on the return line below the pump and yes I believe that anything I run into the boiler will run right back out using the fill valve. I plan on flushing by running water into the relief valve fitting and draining through the bottom. Thanks for all the suggestions, I doubt I will be doing much before Christmas. Maybe the beginning of next week. Merry Christmas and I'll post after I try a few things. Thanks again..................0 -
steam
Chevy, What is the water pressure in your system? Is the expansion tank water logged? and does it have the proper precharge?
Remember in the old days when your car engine boiled over if you did not have a pressure radiator cap?If the heating system pressure is low and if there is air in the system and sometimes when the circ pump operates the water will boil at a lower temp.0
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