Replaced a zone control valve in a hot water boiler (Weil-McClain), turned on system and bleed system from each spigot. Boiler pressure got extremely high, turned off fresh water inlet-supply, drained some water out of system and brought pressure down to 20-25 psi. Has held fairly steady now for a few weeks. Afraid to turn fresh water supply back on for fear pressure will build again. I did loosen the schrader valves, one on the pressure tank and the other on top of the boiler, only water dripples out. Turned the one on top of boiler closed as the water was going into the boiler and on the floor. Should I open the fresh water/refill valve to see what happens? Can always drain off enough water to bring pressure down. Can air in the system cause high pressure? Can too much water in system cause high pressure? The only pressure gauge I have showing this is the one on the boiler. Thanks for any help with this.

 

In a hot water boiler, (not a steam system), you can not have too much water. The system is intended to be FULL of water, and no air at all.

If you have air in the system, it won't cause the pressure to be high. You will hear it circulating in the system though, and it may cause a zone or heating loop to not put out any heat.

You CAN have too much pressure though... and it seems that you do. 20-25 is too high.

There are basically three things which can cause high pressure in a boiler system.

1. Waterlogged expansion (or compression) tank. There are two types, one looks like a propane tank and hangs from the piping. There is a diaphraghm (or bladder) in this type of tank. The other is a steel tank strapped into the rafters above the boiler. Can you tell which type you have ?

2. Defective or mis-adjusted pressure reducing valve. This is the bell shaped thingy that is in a line between your domestic water supply and the boiler water system.

3. IF your system has a tankless water heater coil, that coil can leak and cause the pressure to rise. If you have this type of water heater, it is not likely your problem because you say the pressure holds when you turn off the manual feedwater valve.

If you have a one or two story home, start by dropping the boiler pressure even further. 12-15 PSI is normal.

If you have water constantly leaking out the schrader valves on the automatic air vents, they are defective and should be replaced.

 

Thanks, I have the one that hangs and looks like a propane tank, with a schrader valve on top of it that has leaked and rusted the top of the tank. My wife says I should clean it up and repaint it with some rustoleum.

How do I detemine if the bladder tank is bad? Like I say the schrader valve leaks, can a bad tank cause the valve to leak?

Thanks again for your help

 

Valve at the top? Can you posts a pic?

 

As 'Who' said, a picture would help, you can post pictures on www.photobucket.com (free) and provide a link here for us to view. This would save a lot of typing... I think I know what you mean by your description, let's make sure though...

The tank is hanging off a hunk of cast iron, right ? (that would be your 'air scoop')

On top of the air scoop, there is a brass can, with a schrader valve on it, correct ? If so, that can would be your 'automatic air vent'. And that schrader valve is leaking, correct ?

Is there another cap on the bottom of the tank ? and if you remove that cap, another schrader valve ?

If my description fits what you have, then the answer to your question is no, a bad tank won't cause your air vent to leak. They do a good job of that all by themselves!

Is there a shut-off valve in between the tank and the air scoop ?

Here's what you can do ... TURN OFF BOILER AND LET IT COOL TO ABOUT 100*F. Keeping the feed water valve closed, drain enough water from the boiler to drop the pressure to zero in the boiler. Using a GOOD QUALITY tire pressure gauge, test the pressure at the schrader valve on the end of the tank that is opposite to where it is attached to the system. If it is below 12-15 PSI, using a small air compressor or bicycle pump (if you feel strong) add air to the tank until it reads 15 PSI.

Open the feedwater valve until the boiler pressure gauge reads 15 PSI.

Turn boiler back on and run it while watching the pressure gauge. It should not increase more than 3-8 PSI from cold to hot.

Your tank pressure is probably NOT your immediate problem though. I'm guessing that the pressure reducing valve is leaking through.

If wifey wants the tank painted, then paint it... or just go ahead and replace it with a new one.

 

I will try find a camera, I don't think a cell phone camera will do very well.

As I recall the "hunk of cast iron" is a pipe that goes into the boiler. Not sure if it is the return pipe or the hot water pipe coming out. I am getting some popping and clunking noises when the hot water starts to circulate. This was after opening the system and replacing the zone control valve.

Everything you said is correct, except that I will have to see if there is a cap and another shrader valve on the bottom of the tank. There is no shut off valve between the tank and air scoop, just a piece of galvanized pipe connecting them.

Also, I unscrewed the caps on the schrader valves, and I do not think that they are like a tire tube valve, where I could test the pressure like a tire. So if that is the case, then they really are not schrader valves? Will check out closer.

Where is the pressure reducing valve and is there anyway to check it?

OK, I looked back at your previous message, and this is the bell shaped deal on the inlet water line. So my stupid question is......if you can't have enough water, how does this cause a pressure problem? Won't it just keep the water on?
Pressure was not an issue before replacing the zone control valve. Seems like I fix one thing and either break or cause something else to fail.

I am guessing that with a closed system such as this, that when you open it open it up, you open the spigots to bleed off the majority of the air and then within a certain period of time, the schrader valves take of the rest?

Sorry but I am at work and the boiler is at home. Thanks again for you time and help with this.

 

A cell phone pic is better than nothing, but only barely!

Probably the noises you are hearing are air passing through the system. Since you replaced the zone valve, you got air in, that is still in there.

Right about the other 'schrader' valves. You can't _nor would you want to!_ put air IN there. Those are basically a 'float' valve. When that can fills with air, the float drops and lets the air out, water comes in, lifts the float and closes the valve. It's very much like a schrader valve, but serves a very different purpose.

The one on the bottom of the tank IS a schrader valve and is intended for use with a tire gauge and filler.

You can't have TOO MUCH water... but you can have too much pressure. The 'pressure reducing valve' is basically a 'regulator' that is set to the pressure that your system requires, typically 12-15 PSI. When the pressure in the system gets to the set point, that regulating valve closes and won't allow any more water in. If there is a leak, or if you bleed air, and the pressure drops, it will open and let just enough water back in to bring the pressure back up to where it belongs.

Since for the past X number of years that pressure reducing valve probably hasn't moved much, it had a chance to build up some 'crud and corrosion' on the internal parts. When you drained the system to replace the valve, that crud got loose, and into the innards of the valve causing it to malfunction. Not your fault, it happens...

You actually have already checked that valve. When you closed the manual valve, and the pressure held steady, that means the reducing valve was leaking through.

Since you don't have a valve between the tank and the boiler, what you can do is drop the boiler pressure to zero by opening a drain and letting out just enough water to drop the pressure. You don't need or want to DRAIN the boiler, just drop the pressure. THEN you can check the air pressure in the expansion tank, and adjust it if necessary (it will be necessary...) Open the manual valve to bring the pressure back up to 12-15 and you can run the system that way until you have a chance to replace the reducing valve. Make it a point to CHECK THE PRESSURE from time to time if you do this!

Your assumption about getting the majority of the air out is basically correct. Sometimes you may have to go back later and bleed some more air because the fresh water you put in has air in suspension that won't come out until it gets heated up. It can sometimes take months to get ALL the air out. But for the small amount that's flowing through the pipes, yes, the automatic vents should take care of that.

You may have to find the bleeder valves on your radiators/baseboards, and open them to get the stubborn bubbles out, since air will find the high spots in the system and not want to go back down. Hopefully your system has bleeders on the radiation.

Happy New Year!

 

I had asked the plumber about the leaking "schrader" valves and he had said to tighten the cap down, but wouldn't that defeat the purpose of bleeding off air? I am taking it that I should replace the whole valve and not just the caps on those, correct?

Is it a good idea or a bad idea to put some heat on that regulating valve to see if that clears it up? I say this because on the zone control valve, replacing the power head did not fix it, but by the time we sweated off the old and had it apart, you could see the ball valve inside, opening and closing. Makes me wonder if all I had to do was put some heat on it and not replace it!?

I checked and my radiator/baseboards do not have bleeders on them.

How do they get all of the air out when the intial system is first installed and fired up?

Also, if my system pressure at the pressure tank (well) is 40psi, how can it get any higher than that in the boiler system? At one point before I shut off the water coming into the boiler it was over the red mark, must have been 100psi or higher!

Thanks again and have yourself a Happy New Year's!

 

If your pressure went to 100 PSI, and your safety relief valve didn't open, you got big problem keemosabe... more on that in a minute...

Yes, it will defeat the purpose. If they leak water, they need to be replaced. Once a system is relatively air-free, you can generally get away with closing them, because the air is out ... then maybe once or twice during the season, you can open them to manually vent any air, then close them again. But for what you need to do now, you should replace them.

Heat on that valve is definitely not a good idea. There's plastic and rubber parts inside... you'll make it worse.

In a perfect world, every boiler installation would have 'purge stations' installed at the boiler. A ball valve with a drain above it so that you can purge the air out. See the pics in this thread : proper purge stations

Do you have something like that ?
(waiting for pics... tomorrow I think!)

About that 100 PSI... that is a VERY dangerous situation if the pressure was indeed that high. However, I would first question the accuracy of the pressure gauge on the boiler. The first thing you need to do is verify that gauge. You can get a gauge at HD or Lowes that screws onto a hose fitting. It's not good for low pressure, because the range goes to like 200 or so... but it will tell you if that gauge is reading correctly or not. They go for like $10 and are used by lawn sprinkler dudes to check pressures, but they work great on a boiler too. Ones I've seen are made by Watts.

If you actually had 100 PSI in that system and your relief valve didn't open, then that is the next thing to do... replace the relief valve... do not neglect it!

You can have more than the supply pressure because water expands as it's heated. (around 4% by volume) Your expansion tank absorbs most of the expansion so that the pressure does not go out of control. This is why it's important to make sure you've got the correct air charge in the tank.

By the way, the fact that you are on a private well leads to higher chance that a piece of debris got in that reducing valve. I live with a well myself, and my reducing valves only work properly for 5 years at the most.

 

Thanks, Trooper.

I will check some of this out, see if I can get some pics after the New Year's.

I looked at the pics in the bucket, familar stuff, but mine is set-up a little bit differently.

 

Finally getting back, sorry Trooper didn't mean to get you excited...but I did misread the pressure gauge. Pressure was in the 40 to 50 range, still too high. I do believe that the fresh water pressure reducing valve needs to be replaced, as the pressure will hold steady with the water valve shut off. Been too cold here (Montana 15 below) for a neophyte like me to be monkeying around with the boiler. I did however, replace the airvents and they have/released some air. Still getting noises and hammering/banging in that zone. My question is, is it ok to first increase the pressure in the system to say 25psi and let run for a day or two to see if that will push some more air out before hooking up a hose and flushing the zone? My system also has the antifreeze solution in it and one of the zones has a small (4 or 5 feet) base board heater in the garage to take the chill off. Other than the noises it is heating fine. If you think that the air may work itsself out with the new air releases, how long might that take? Thanks Much