How to increase pressure in hot water heating system after radiators are bled?

ThisSemiOldHouse

Hi, I am a new homeowner... moved into this house about 15 months ago. The house was built in 1908 and is a three-story house (plus basement). It has a relatively new Weil-McLain gas-powered hot water heating system in the basement, that distributes heat throughout the house via several older cast-iron radiators and baseboards (to be exact, there are five cast-iron radiators and one baseboard on the first floor, three cast-iron radiators and one baseboard on the second floor, and no heating on the third floor). The heating system is controlled via a Honeywell digital programmable thermostat located on the first floor.

Since we moved in, I haven't done anything to maintain the radiators or the heating system... except, of course, to switch on the thermostat during the cold months last year. Throughout that period the heating seemed to work OK. This year, however, when I turned the system on (which was about two weeks ago), I eventually noticed that two of the radiators on the second floor do not get warm at all. So I Googled it and learned that the radiators throughout the house probably all needed to be bled, since that hasn't occurred at all during the 15 months that we've resided here. So, I bled all of the radiators and baseboards earlier today. Yesterday I also separately noticed, before even shutting the heating off at the thermostat and bleeding any of the radiators, that the pressure gauge on the Weil-McLain unit was consistently reading out at about 8 psi throughout the day (i.e., with the heating system on and running), which in my opinion seems low. The unit has a pressure-reducing valve with a fast-fill lever currently set to its horizontal "off" position. Pretty sure the pressure-reducing valve is preset to 12 psi, so I'm not sure why the boiler's pressure gauge is reading at 8 psi (perhaps it was reset at some earlier point?). And then right before the pressure-reducing valve is a water shutoff valve that is set to its closed position, which I'm assuming is the valve that, if opened, would add water to the boiler.

So, taking all that into account, and since all the house's radiators have now been bled, I had a few questions, as follows:

(1) I would now like to increase the pressure in the boiler so that it reads out at the proper level. (Speaking of which, for a two-story house, I understand that the optimal level should be 12 to 15 psi — is that correct?) To increase the pressure, I'm assuming that I would have to temporarily open the water shutoff valve that's located immediately before the pressure-reducing valve, until the needle on the boiler's pressure gauge reads in the 12 to 15 psi range. Anyway, if that's the correct procedure, what I was wondering is this: *before* I open the shutoff valve, do I need to change any setting on (or otherwise make any adjustment to) the pressure-reducing valve? For example, does its fast-fill lever need to be moved to its vertical position, or can it be left as is? Also, might the pressure-reducing valve need to be reset in such a way so as to increase its existing set value? (I ask this because if the boiler's pressure gauge is currently reading out at 8 psi, then I'm wondering if the pressure-reducing valve is either not working properly, or if its psi value needs to be increased.) Or, can I just leave the pressure-reducing valve as is?

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(2) When bleeding the radiators on the second floor, I noticed that even though hissing air came out of one, it was followed by no water whatsoever. And then with one of the other second-floor radiators, not even hissing air came out of that one (not to mention no water, as well). Will these two radiators need to be re-bled after the pressure in the water boiler is increased to its proper level?

Any info would be helpful. Thanks!

Intplm.

Seems your PRV needs to be adjusted. How that is done depends on the type that you have. Some pictures posted here can help.

As to bleeding your radiators. You will certainly need to add more water, or more pressure to your boiler to properly bleed those stubborn rads on the second floor. They are higher than the first so your situation is typical.
I add as much as 25 psi to a boiler in this situation and bleed the water out at each rad. The pressure will go down as you bleed the water from the rads., replacing the air in the rads with water.
Use your fast feed to raise the pressure. You might need to do this a few times to get all of the air out.

And maybe post some pictures as to what your boiler looks like with the type of auto feed that you have, expansion tank, circulator(s) and or zone valves.

JUGHNE

You should be able to open the supply valve to the PRV and it should add water to the 12-15 or whatever it is adjusted too.
If you lift the lever that is full house pressure into the system.
That would be used to fast fill an empty system.....but if left open it would open your pressure relief valve which is set a 30 PSI.

With the supply valve open and your pressure at that 12-15 PSI, you can bleed more air and should get water.
8 PSI will raise the water up about 18' above the boiler. It will push air out but the water will not go higher than 18'.
Some pressure gauges are also showing altitude....8' = 18'...15PSI = 35'. With the 18' you were probably close but not quite there up to the air bleeder.
Then with the 15 PSI that will compress the air in your exp tank.

It does not hurt to exercise the fast fill lever a little. Sometimes the auto fill portion will stick and that raising and closing the lever may loosen it.

It is usually common to leave the supply valve turned on.
Bad if you develop a leak, worse if off and you run out of water and the boiler fires dry.

Intplm.

@JUGHNE . It depends on the style/type of PRV he has. There could be a sliding lever as Taco provides. A up or down lever from Watts, or a older screwdriver type of adjustment.
Seems from his description that he has a much older system. That's why I asked for some pictures.

JUGHNE

He mentioned a fairly new boiler system and also a fast fill feature that was set to off.
But, I too am waiting for pictures........ .....always necessary.

Intplm.

Yup. But he is bleeding different older rads, I'm wondering what he's got. The pics will eliminate the confusion. Hope that he posts some. ?

ThisSemiOldHouse

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ThisSemiOldHouse

Thanks so much for all the comments posted thus far, and sorry for my delay in adding pics. Here are a few (see attached images). I've included a pic of the front of the Weil-McLain unit, as well as a handful that were photographed from the unit's left side, which show the pressure-reducing valve, as well as the closed water shutoff valve that I'm guessing supplies water to the boiler (see valve in upper left portion of the related photos). I've also included a close-up of the pressure-reducing valve, and another of the boiler's pressure gauge. The pressure looks to have now fallen to around 6 psi, following the radiators being bled. The heating system is still switched off, as it was when these pictures were taken. One new and concerning development that I only noticed while taking these pictures a few minutes ago, is that there is now a slow water leak coming from a long vertical pipe toward the left rear of the unit. In my photos, the pipe I'm referring to can be seen in the most wide-angle pic of the left side of the unit. It's leaking at a rate of approximately one drop of water per second, and only began happening after I shut the heating system off and bled the radiators a few hours ago. Nothing like that has happened during our 15 months residing here. Leak is still going now... and as shown in the pic, I put a tall water glass under it. What, if anything, does this leak indicate, and what should I do to fix it? Thanks again.
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STEVEusaPA

What kind of expansion tank do you have? This may make a little bit of a difference in how you purge the system of air.
Also, it’s not a bad idea to make sure the gauge is working properly.

ThisSemiOldHouse

Thanks.

In preceding comment, the expansion tank is visible in the second photo from top, and — partially, at least — in the lowermost picture, as well. (Can post additional pics of it, as well as pics of the radiators, if either might help.)

How would I test the gauge? Agree that that would be a good idea.

STEVEusaPA

Didn’t see you pics until after I posted. I have a stand alone gauge that attaches to a boiler drain, similar to this:
http://www.webstonevalves.com/default.aspx?page=customer&file=customer/wecoin/customerpages/AddAGauge.htm

With the system off, add water to get the pressure up to 25lbs, like @Intplm. mentioned. Have someone keep the pressure up while you bleed.
When you’re done bleeding, run the circulator for a couple of minutes without firing the boiler. If you can’t, it’s ok to run it for a few minutes. It won’t heat up that fast.
Shut down system, bleed all rads again.
Then go back to the basement, and drain off a little water from the drain until you are back down to 12 psi cold.
Turn boiler back on.

Intplm.

The leak is your pressure relief valve discharging. That relief valve will discharge at 30 psi. Or will weep because it is showing its age. I would get it replaced.
The gauge may also need replacing. Can't tell if it is giving the correct information. So, while you are at it, change the gauge when you change the relief valve.
After that is done you will then be able to see what your auto feed is doing by reading the new gauge.It should, as you now know read 12-15 psi. If it is reading to high (30 psi) then your relief may begin to discharge again.
What I would do is: replace the gauge, replace the auto feed /prv and the relief valve.
This should stop the leaking relief valve and allow for more confident and accurate purging of the radiators.

One more thing.

Make sure your expansion tank has a air pressure charge of 12-15 psi. ( see the air valve, like a tire valve on the tank ) Carefully press on the air valve. If air comes out, add air to the correct pressure mentioned.
If water comes out. The tank has lost its diaphragm and its air charge.. If it has lost its diaphragm then the tank will also need to be replaced.

I know this is a lot to take in but these components are all integral with each other. If you go to the trouble to change one, might as well shange them all. Especially if they are as old as some appear to be.
And what @STEVEusaPA said.

ThisSemiOldHouse

^^^ Thanks for all this info; it's a huge help!

Just out curiosity, between now and the time I replace the relief valve (hopefully tomorrow), is there any immediate thing I can do to stop the slow leak?

Intplm.

No. Do not try to plug or manipulate the relief valve in any way. It is your best safety device. It protects against damage to the boiler, your home and most importantly, You.

JUGHNE

If you have a floor drain close.....you can lift the lever and discharge full flow......often there is just some debris under the seat, then let it snap back in place. This could be done 2-3 times and it might reseat and then again not. So if it is only a drip leave well enough alone.
I test/flush these at every PM.....but I have a spare on hand.
If flushed every year then no problem, but if never opened for flushing then maybe a drip.

And the air pressure in the tank can only be checked or adjusted when there is no pressure in the system. Then the tank should "feel" or sound empty.

If you get a pro in there he should know what is going on.

Intplm.

^^^^^^^^^^^^Excellent advice^^^^^^^^^^^^^^^

ThisSemiOldHouse

Thanks. I might have to do that (i.e., have a professional take a look at it). For the record, most of the terminology discussed thus far is new to me at best, and Swahili to me at worst [laughs]. (Whereas if someone were to ask me to transcribe a difficult guitar solo, that I could do with no problem, lol.) But even basic boiler repairs are a whole new field of knowledge for me.

I can't help, though, but be struck by the coincidence of the leak occurring shortly after bleeding the radiators. What I mean is, this is the first time something like that has happened in fifteen months, which is the whole time we've been here. So, what specifically about bleeding the radiators would result in the relief valve discharging, particularly if the heating system was switched off throughout? In other words, I could understand that happening if the pressure had increased for some reason... but if anything, the bleeding of the radiators appears to have caused the gauge reading to drop by about 2 psi. So, just wondering about that.

JUGHNE

BYW, take a screwdriver and rotate that red needle into the temp portion, (it is just a marker/indicator), get it out of the way of the pressure section. You see the PSI and feet of H2O relationship?Then take the screwdriver and tap on the side of the gauge (professional secret BTW, learned from submarine movies) . When you open the fill valve you should see pressure rise, this is just an indication that your gauge may be working.

Why the drip now, maybe the change in pressure and then the boiler being cold perhaps.......might stop when hot??

Intplm.

How long did you have the boiler off before starting it up again? A short time? Or was it for a few months?

ThisSemiOldHouse

The heating system had been shut off since approximately early April 2019. Then I turned the system back on about two or three weeks ago. It has remained continuously on since then and has generally been working fine, with the exception of two of the cast-iron radiators in the second-floor bedrooms, which have been cold throughout. (The third cast-iron radiator on the second floor has, however, been working alright over the last two weeks, as has the baseboard in the second-floor bathroom.)

I guess my main concern right now is that I don't want to do anything that might exacerbate the slow leak (since, as was pointed out above, a slow drip would — until a pro checks it out — definitely seem to qualify as a "leave well enough alone"–type scenario). But in all honesty, I *am* curious to see what would happen if I were to open the water supply valve (which thus far I haven't done) so as to increase the pressure by a few psi, and then also turn the system back on afterwards. Would doing that have an effect on the leak? If so (and I would think it's certainly possible), then I'd just as soon hold off and just let the water glass currently sitting under the relief-valve pipe continue to collect the dripping water until a plumber shows up here. Right now the leak is producing about half a glass of water per hour.

HomerJSmith

Open the red handled valve before the double check backflow valve. Perhaps the valve was shut off because the vent on the double check valve was dripping.

Pressure in the system should be 1psi for every 28" from the top of the boiler to the top of the highest radiator on the highest elevation (3rd flr) + 5psi. You can measure it, but I would suggest 17-19psi, cold. The air charge on the expansion tank should be the same as the setting on the fill valve (sys. pressure).

Since you have to drain down the sys water to replace the PRV, take the opportunity to check the air charge in the Xtank. Use a cheap digital tire gauge.

ThisSemiOldHouse

^^^ Thanks for this info. When we moved in, someone (the realtor, perhaps?) told us that the one radiator that's on the third floor "doesn't work," although an hour ago I asked my girlfriend if any information more specific than that was given, and she said no. So, it could be that the radiator in question *could* actually work, but the house's previous owner either never bled that particular radiator or didn't know how to adjust the pressure on the boiler. I hope to look into it further, although we're currently using the room in which that radiator is located as a storage room, so at the moment I would have to move some furniture around to even get to it.

To follow up on my previous comments, at about 10:30pm (about four hours ago) my curiosity got the better of me, so I did actually go ahead and do what you just suggested above: namely, I opened the red-handled shutoff valve. I kept my eye on the pressure gauge to see if this would get it to move from its then-current value of 6 psi up into the 12 to 15 psi range, but if there was any effect at all, it was almost imperceptibly slow. So I lifted the fast-fill lever on the pressure-reducing valve to its vertical position and then you could really hear water flowing. The needle on the pressure gauge likewise moved a lot quicker when that handle was raised. At any rate, I waited until the gauge read out at approximately 14 psi, and then I put the fast-fill lever back to its horizontal position and also closed the red-handled water shutoff valve above it. And then last, but not least, I went back to the thermostat and turned the heat back on.

Anyway, that was about four and a half hours ago. Thankfully, following the above steps actually wound up stopping the slow drip from the relief valve drainage pipe. Not sure why. That happened about half an hour after I turned the heat back on. The drip fully stopped, and it's been that way for nearly four hours. I also monitored the temperature and pressure on the gauge throughout the boiler's various heat cycles. I would say after several minutes of a heat cycle, the pressure tops out at around 18 psi. And then during intervals when the boiler is not hot, it goes down to around 14 psi or 15 psi. So, it seems to be working properly. I'll continue to observe how it's working over the next few days, hopefully it'll stay as is.

As for the radiators, particularly the ones on the second floor that were not warming at all — those two radiators are now emitting heat. Although for now, the tops of them are not really too hot. But neither of them was working at all until about four hours ago. The lower portion of each of those two radiators is unmistakably working now, you can feel the heat if you reach down. As I think was suggested in one of the earlier comments, I'm thinking at least those two radiators might need to be re-bled so that the tops of them actually radiate heat, too. But just the idea that they're now even working at all, and that the slow drip from the boiler has stopped, are both at least a step in the right direction.

Thanks to everyone who weighed in on my original questions; I really appreciate the input.

ThisSemiOldHouse

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Intplm.

You may just have a poorly seating relief valve. Or some debris is caught in the way of it seating properly.
Go ahead and fill the boiler to 15 psi and see if it increases.


Also. In the future, let your boiler maintain its required temperature year round. This will help to maintain your boilers integrity. It needs to work. By shutting it down for such a long time expansion and contraction issues have helped your boiler to leak.

JUGHNE

If you want full heat out of the 2nd floor rads you will have to bleed the air while keeping the pressure up.

Now if you have a 3rd floor rad and it is still connected to the system, if you get some water in it but not enough heat to keep it from freezing then that is a problem.
You would have to raise the pressure higher to fill the 3rd floor rad. If you do not bleed it then the water across the bottom will circulate and remain hot.
You can shut the valves off but originally the valves were designed to not completely shut off the water flow. There should be a small port in the valve that allows a minimal flow of water to prevent freezing.

I service a 2 story house with 6 bedrooms upstairs. Only the lower level is in use as an office. The second floor rads are all valved off as much as possible. I make it a point to not bleed all the air out of the rads, except for the bathroom.
This saves fuel as the rad only get warm on the bottom and the room is cooler.....less heat delivered......but freeze prevention is accomplished.
You could do this for the 3 rd floor and even drape a quilt over the rad to keep the heat in the system if you want no heat on the 3rd floor.

But as it is now that 3rd floor rad may stay dry and full of air, however if the pressure is raised and enough water gets up there but not enough heat to prevent freezing of the piping and rad then that is an issue to consider. If the piping is buried inside an outside wall it could be half full of water that is not moving.

That PRV is easy to adjust: open the supply valve....hold the screw on the top with a screwdriver.....loosen the locknut underneath it.....when you turn the screw in it raises the pressure (backwards from what you might think)...go one full turn in with the screw. You may hear water slowly going in....watch the gauge. This is a slow process.
If the PRV is working it will shut the water flow off when the pressures rises.
If you want more pressure....go another 1/2 in with the screw.
When satisfied you lock the nut back down.

Then as you bleed air the PRV will add more water to fill the rads.

If you want to get the water to the 3rd floor you may have to raise the pressure to maybe 17 PSI.

ThisSemiOldHouse

UPDATE: So here's what I wound up doing:

Yesterday afternoon I wanted to get an idea of exactly what the distance between the basement boiler and the top of the house's highest radiator was, so I physically measured it as accurately as I could. The distance between the two was just over 29 feet.

Then, last night I re-bled all the radiators throughout the house, but before I began (and with the heating system shut off at the thermostat), I opened the fill valve to raise the boiler pressure to approximately 18 psi. I also made sure to start with the radiator on the highest floor, and work downwards in bleeding each of the remaining radiators.

This time around (presumably because the starting pressure was considerably higher than when I originally bled the radiators yesterday, at which point the boiler gauge read out at around 8 psi right before I began), the bleeding process was like night and day compared to last time. The radiator on the third floor, for example, seemed like it was hadn't been bled since Eisenhower was still in office. The sheer duration of the hissing air sound from that one probably went on for a solid three minutes, or possibly a bit more. Then water finally started to flow out of its bleeder valve. But in the process, the system wound up losing about 7 psi from bleeding just that one radiator alone, so I went back to the basement and refilled the boiler until the gauge read out again at 18 psi, before starting to re-bleed each successive radiator. The ones on the second floor also behaved differently this time around (again, presumably at least, because the starting pressure was a good deal higher this time). When I originally bled two of the second-floor radiators yesterday, for example, no water came out of either. This time they hissed for a while, and then both discharged a strong stream of water.

Anyway, after I was done re-bleeding all the radiators and repeatedly going downstairs (at least at first) to re-raise the pressure reading on the gauge via adding more water from the fill valve, I turned the heat back on at the thermostat. A few minutes later I then went up to check how the third-floor radiator and the second-floor radiators were performing. Thankfully, they all got hot, and more importantly, each of them was emitting heat all the way up to the top of each radiator, which was not happening at all until now. But, I still wanted to go back downstairs to check what the boiler gauge was reading, both pressure-wise and temperature-wise. What I observed got me a bit concerned. You see, when I initially switched the thermostat back on, the gauge read out at approximately 18 or 19 psi, and since the heat had been switched off for a few hours, the temperature reading was as low as the gauge goes. At any rate, for however many minutes the heat was on before I went back to the basement to check the boiler gauge, the pressure had risen from 19 psi to approximately 28 psi, and the temperature reading was, if I recall correctly, somewhere around 190 or 200 degrees Fahrenheit when I got down there. So, my main concern was that 28 psi doesn't exactly leave too much room for error with regard to the boiler's pressure relief valve kicking in at 30 psi, and I didn't really feel like just waiting and watching the levels rise any further (particularly if the end result would be a flood), so I shut the heat off again at the thermostat and then waited a little while for the temperature reading on the gauge to come down. Once that happened, I drained some water from the boiler (not very much, actually) until the pressure reading went down to approximately 15 or 16 psi. Then I turned the heat back on.

Since I did that, everything now seems to be working the way it should. To be precise, when boiler receives a call for heat, the gauge values start out at around 88 or 89 degrees Fahrenheit at 16 psi, and then during the ensuing heat cycle, the temperature rises to approximately 159 degrees and then the boiler shuts off. By that same point, the pressure appears to go up to around 18 or 19 psi. Another thing I noticed is that after the boiler shuts off, the temperature reading keeps rising for a minute or two and ultimately peaks out at approximately 170 degrees, after which it begins to fall steadily back to around the 110-ish degree range.

Which brings me to a couple of questions:

First, are the above-listed temperature and pressure values (I mean the ones from *after* I drained some water out of the boiler) normal values? That is, do they represent normal boiler performance? (For what it's worth, all the radiators on the upper floors now seem to be working perfectly.) Also, if the preceding temperature and pressure values — as well as their above-listed ranges during a typical heating cycle — are "not" normal, them what should the optimal temperature and pressure on a boiler be during a heating cycle, and how much should those values vary between the beginning of the cycle and when the boiler eventually cuts off?

As always, any insights are greatly appreciated; thanks in advance.

Jamie Hall

I'd say that you've finally got the thing working the way it should! Congratulations -- isn't it a good feeling?

And yes, in a three story house there is remarkably little headroom between the required operating pressure and the pressure relief valve setting. But with an adequate expansion tank -- which you seem to have -- it works.

The only thing I'd add is that you check and make sure the cold pressure really is holding over time. But it's worth looking at the system from time to time anyway, and this just gives you a good excuse to do it!

JUGHNE

As you see water expands when heated.....it cannot be compressed like air. So the reason for the air cushion tank.
The size of the tank is determined by the amount of water in the system which is determined by the radiator size and piping.
Your old rad system typically needs a larger tank than normal.
Some of your rads were contributing air cushion by holding a "head" of air at the top of each.....especially the 3 rd floor.

The more air cushion then the less rise in gauge pressure as the water expands. The charge in the tank should equal your cold pressure charge.

Can you isolate the tank without draining the system?
Pictures of tank needed.

mattmia2

It is possible whoever installed the tank never adjusted the default 12 psi for the higher pressure for the 3 story house or a little bit of air has leaked out. You can see the bottom of it in one of the pictures but a picture of how it connects to the system would tell us if you can adjust the pressure without draining the system. It seems like the charge is a little low, but it is also probably a smallish tank for the system size.

ThisSemiOldHouse

Here are some better pictures of the expansion tank. It's made by Amtrol, and its label identifies it as an Extrol Model No. 60. For what it's worth (and as is shown in one of the more close-up pics), a portion of the label text says: "Do not adjust the pressure or re-pressurize this product except for any adjustments at the time of the initial installation when the product is new."
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JUGHNE

Can you post a picture showing all the piping including all the valves?

HomerJSmith

You need to check the air charge on the X tank and set the pressure to the sys pressure about 18-19 psi. You need to drain down the pressure or water in the system and typically remove the tank or sometimes it can be air charged in place.

Remove the blue cap on the bottom of the tank and use a small compressor or pump and pump air into the tank to 19 psi. If a lot of water comes out of the tire valve when you depress the stem, you may need another tank. Use a digital tire gauge to measure the air charge. Refill the sys and re bleed the radiators.