Short cycling boiler. I'm stumped.
Comments
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Ok. ::update::
I opened all the ball valves and started her up. I began to count to 5 as the burner came on.
No short cycle.
I went up stairs and set the 2nd floor thermostat to call for heat. Turned my first floor down so it wouldn't.
I noticed the pressure rising pretty close to 30 PSI so I threw my short hose on one of the zones and cracked the globe valve just a little to bring the PSI down to 25.
I noticed the heat suddenly pull back some. I'm not sure if it was due to the 2nd floor call for heat. The zones were both cold to the touch for a while as the temp went to 170 + but i started to hear one zone making some noise in the pipe. I felt it and it's now nice and hot. I went back up stairs to first floor and set it to call for heat. Now both zones are screaming hot. Burner still running. Gage looks like this ...
I keep cracking open the 6 ft hose into the bucket, though, to keep the PSI away from 30 so my safety relief doesn't pop.
Question..
Where should my PSI sit @ when this temp hits 190? I've got it to sit at 25 PSI. Is that ok?
Also, another update.
It hit 190, burner shut off. I went upstairs. Heat hot water, yay! But I wwent back down to it short cycling at 170 degrees again. Seems like it stopped short cycling quicker than the usual and we're sitting at 175ish
Not sure what to think but I'm so greatful we're back online over here.
Thanks everyone
I'll look into what ED said.
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Not that high; maybe 18PSI. Did you check the expansion tank before you refilled system?
Make sure you don’t have a valve closed on line to expansion tank. Do you have pictures of that section of the piping?1 -
Do you see that gray tank up by the ceiling"
Tap on the side of the tank near the bottom with a hard mallet or a soft hammer. You are listening for whether the tank is full of water. If it is full of water, you will get a very dull thud. If it is not full of water you'll get a very soft tapping sound. It is a bit difficult unless you are skilled.
The problem is most likely the tank has filled with water and provides no "cushion" for expansion.
When you start at 15 psi, it should NOT rise more than 20 psi if the tank is working properly.
I am making the assumption that you purged all zones properly and there is no residual air.
Lower the pressure to 20 psi when the boiler is fully hot (190°). Then when there is no demand for heat and it cools all the way back to room temperature, read the pressure and advise.
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Ed will help you with the short cycling. He's familiar with that fan unit.
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@LRCCBJ Has done a great job getting you this far. I noticed that you have a Extrol expansion tank. This tank is supposed to keep the water pressure in your boiler form going too high when the water heats up. I see that you got close to 30 PSI when the water got above 180°. That could be a problem with the expansion tank. You are going to learn about expansion tanks today.
So to be clear with your system, when you fill the boiler to 15 PSI, the expansion tank should also have 15 PSI air pressure in it. That means that there is no water in the tank and both sides of the membrane that separate the air from the water are at 15 PSI. Your boiler may have about 20 gallons of water and the radiators and pipes may have another 10 to 20 gallons of water in there. So let's just call it 40 gallons in the system at 60° cold fill pressure. When you get the water to 190° and you add almost 4% more water by volume because the water expanded there is now 41.6 gallons of water in the closed system.
The only place that water can go is in the expansion tank since the system is closed and the backflow preventer (Watts 9D) won’t let any water out. So when the 1.6 gallons goes into the tank that is full of air pressure, that water will compress that air as it moves the air out of the way to make room for the water. The pressure will go up about 2 to 4 PSI. That is normal. When the water cools down after the heating cycle is over, then that pressure will drop down to 16 PSI or 15 PSI as the air pressure in the tank pushes the shrinking volume of water back into the system.
I hope you have followed me up to this point.
Now what if the tank only had 6 PSI of air pressure in it? Whe you put 15 PSI water pressure in the system, the water pressure was higher than 6 PSI and started to compress the air as more and more cold water enters the tank. You may have added 2 to 3 gallons of cold water to the system that ended up in that tank in order to compress that air pressure in the tank from 6 PSI to 15 PSI. That tank is only about 4.5 gallons total.
With the tank more than half full of water when the boiler water is cold, there may only be about 1.5 gallons of air space left in that tank. So as the water expands to 1.6 more gallons of water, there is less room for the water to expand and that air cousin will increase in pressure until the relief valve pop off pressure is reached and you end up with a puddle of water on the floor.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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Now to get the expansion tank correct, you need a tire gauge that will measure as low as 15 PSI. Then you will drain the boiler (like you are purging one of the loops) with the manual fill valve closed. Watch the gauge drop below 8 PSI and test the air pressure in the expansion tank. You don't need to go any lower than 8 PSI on the boiler gauge because you don't want to let any air back in the boiler since @LRCCBJ just finished telling you how to get all the air out.
If The air pressure in the tank is below 15 PSI then you need to add more air. A bicycle pump is the best way to do this but it may take about 30 to 40 pumps to get to 15 PSI in the tank. If you go over 15 PSI, then just let some air out until you get the tank at 15 PSI. (EDIT) This is not rocket surgery… 14.5 PSI or 15.2 PSI is close enough.
CAUTION If you use an air compressor and it is set for 50 or more PSI, then you want to add short bursts of air and measure the pressure after each short burst. You do not want to get 60 PSI in that tank and over stress the membrane in the tank.
Once you get the tank at 15 PSI then you can turn the manual fill valve back on and let the Watts 1156 PRV put the boiler pressure back to 15 PSI.
I hope this helps
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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One point:
Before you go through the effort to refill the tank with air as Ed mentioned above, take the plastic cap off the Schrader valve (on the very bottom of the tank) and push in the pin slightly. Either you will get air or you will get water.
If you get air, follow the procedure as Ed mentioned above.
If you get water, the game is over and you must replace the tank. No need to attempt to add air……….will not work.
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Nice instructions @EdTheHeaterMan.
@ColdMainer - Are all the valves open allowing access to the compression tank?
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It's weird because I have a pressure gagei tried on it last night and It seemed like the gage didn't wanna work at all on it. I have a compressor sitting down there so I tried it on the gage and the gage responded just fine.
When I test the valve on the expansion tank, air and water come out of it.
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Yes sir.
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Yes, sadly, you'll need to replace the tank. The problem with this is that you'll have to go through the entire draining, refilling, and purging procedure all over again. Sorry………….the pitfalls when the original installer did not include the necessary valves to isolate various components in the system.
The tank is precharged to 12 psi. Raise it to 15 psi before you install it.
https://www.homedepot.com/p/Amtrol-No-30-Expansion-Tank-for-Hydronic-Boiler-EX-30/202268962
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@PC7060 said water coming out of valve is solid indicator of failed tank. You should be able to pick up a new one at local big box.
Ouch. Water from the air side of the tank is a definite sign that the tank must be replaced.
There are two types of expansion tanks You want the one for a closed system that comes pre charged to 12 PSI. They are usually Gray or Green. The other type is for an open system like your hot water heater and comes pre charged with over 45 PSI Pressure. They are often White
When you get your replacement tank, you want to fill the air side of the tank with 15 PSI because the Watts 1156 will make the water side 15 PSI. Check that air pressure before you install the replacement tank. That way you will be sure that you have it set correctly.
For now you can still operate the boiler but it will discharge water thru the relief valve if the pressure gets above 30 PSI. Don't worry, it is only water. You can close off the manual feed valve for tonight so you don't keep adding water after every overpressure event. The operating LWCO will protect the boiler in the event your water level gets too low.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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Ed, do you recommend checking the charge on the tank periodically (provided it can be be isolated from the system)?
I just isolated and drained off my two tanks and found the pressure below 10psi on both tanks. Having said that I don’t recall setting the pressure on tanks when I installed the system 4 years ago 🙈
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I would have used a brass nipple between the PRV and the tee but you already have it on so no big deal.
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You Know , now that you mention it, I might just throw a ball valve in just b4 the expansion tank when I drain it again.
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It's recommended by the boiler and expansion tank manufacturers to check the expansion tank air pressure annually. I do this on all of my boiler maintenance jobs and I have found that the tanks normally lose a few PSI every year. I'm surprised if I find one that still has the same pressure in it as it did the year before.
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The air in the tank will migrate thru the membrane of the tank causing a drop in pressure by about 1 PSI per year. The way it was explained to me is this:
Think of oxygen in the air (it makes up about 21% of the atmosphere) as having its own pressure that wants to be balanced. So when you pump air into the tank, that tank is about 21% oxygen and 78 % Nitrogen with trace amounts of all the other gasses to fill in that other percentage. Now the Air that is dissolved in the water in the boiler also has oxygen in it. But that oxygen gets depleted as it works on rusting all the ferrous metals in the boiler system. Not a lot of rust happens because the oxygen gets used up pretty quickly.
Over a short time all the oxygen that is dissolved in the water will become a part of the iron oxides that make up the small amount of rust that forms. (This is the reason you want oxygen barrier PEX tubing in the system so more oxygen does not migrate back into the system). That is also the reason you do not want to keep adding fresh water with a fresh supply of dissolved oxygen to a closed system regularly. You want to keep that new oxygen to a minimum.
As a result of the oxygen becoming chemically altered into other materials, the percentage of oxygen in the water becomes a lot less that 21% of the content of the air that is dissolved in the water The air in the atmosphere is at 21% and the air that is in the water is at something lower than 21% so there is that unbalance that strives to be balanced. If you have a barrier that allows the oxygen to migrate thru the membrane (like PEX tubing without the oxygen barrier) then that higher percentage oxygen on the outside will get into the water on the inside of the system. That is what is happening with the membrane of the expansion tank. Oxygen is migrating through the membrane. After a year that oxygen migration will account for about 1 PSI pressure drop.
So you need to add air pressure every season in order to keep the tank at the proper pressure.
This may not be the most scientific explanation but it gets the point across to us non-engineer, non-physicist, regular folk.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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Noticed my fan making more noise than usual. I'm gonna take it apart again and see what I can do. I noticed a lot of lights on the board. And one that blinks 4 times.
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