Very old boiler, pressure relief releasing water. acceptable reducing pressure?

[Astro46]

This is likely the original boiler (1926, "The Capitol" size: 25-5), originally on coal, then oil, now running on natural gas, in Chicago, brick 2 story, 2 apt building. About five years ago the expansion tank developed a leak, so I replaced it with an ETX 15 diaphragm expansion tank. After seeing the pressure relief valve releasing small amounts of water constantly during heating season for years, I took it upon myself to lower the reducing valve pressure, eventually to turning it out 2.5 turns. Since then no problem with releasing water, and the system, as far as I know, has worked fine.

This fall I noticed that the Bell and Gossett Series 100 circulator pump bearing housing had water in it. I replaced it end of oct. After that I get a short squeak from housing when pump shuts off. And, pressure relief was dripping for weeks. I tried opening it numerous times thinking maybe rust got stuck in when I turned water back on and flushed pipes through the pressure relief valve. Not getting it to stop, and not knowing if it or the reducing valve failed in the process of turning water off and on, I have replaced both the reducing and pressure relief valves. For about a week after that, water continued to dribble out of pressure relief, so I continued to open it to release move water, hoping to clear it. Water no longer continually dribbles from the pressure relief, but it does release water when heat comes on. maybe 1 gal over the course of a day.

I tried unscrewing the reducing valve adjustment 1 1/2 turns. I have also removed the expansion tank and checked its pressure. 8# the gauge said. I put a pump to it and increased it to 11# and reinstalled it. Pressure relief still releases water. The boiler pressure gauge, after heat being off for 4 hrs shows 10#.

Question is: shall I continue to lower the reducing valve pressure, maybe another 2.5 turns, so it is similar to previous one? Increase expansion tank pressure? Is the current recommendation of 12# pressure not applicable to older systems because maybe the pipes are larger or burners different or ....? Anything bad about having a lower pressure in the system? (With the lower pressure of previous reducing valve, I could still get water (bleed) all the radiators on both floors.)

bonus question: Some sources have suggested that the short squeaking noise at motor shutoff (not all the time) is caused by failing motor mounts. this squeak wasn't happening previous to bearing housing replacement. Local B&G sales reps said if the mounts were bad the coupler would be breaking. That the noise is likely coming from a not quite properly formed sleeve bearing. It may go away, Or I can get used to it. Or replace it under the one year warranty. What do you think about the squeak noise?

 

[Jadnashua]

The system pressure depends on how high up you must pump water. The pressure will decrease at about 0.43#/foot up. You must have positive pressure at the top of the highest run. It's good to have at least a few pounds more. 8# would handle maybe two stories, but 12-15# is much more common. If the pressure goes negative, it will boil and create problems in a vacuum. Water vapor is hugely larger than liquid water and will raise the pressure if things boil (the boiling point lowers as pressure decreases).

 

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[Astro46]

-if radiators can be bled at top, wouldn't this mean that there is positive pressure?

-how would pressure go negative if the pipes are full? in fact, i'm not clear what negative pressure could mean.

-there is a temp regulator attached to the pipe coming out of boilet. currently set to 195. assuming it is accurate and functions correctly, water would not boil, yes?

-why does the system keep releasing water? the overflow tank isn't big enough? looks big enough to hold more than the amount of water that gets released, even if the diaphragm runs through middle of it.

 

[Dana]

-if radiators can be bled at top, wouldn't this mean that there is positive pressure?

-how would pressure go negative if the pipes are full? in fact, i'm not clear what negative pressure could mean.

-there is a temp regulator attached to the pipe coming out of boilet. currently set to 195. assuming it is accurate and functions correctly, water would not boil, yes?

-why does the system keep releasing water? the overflow tank isn't big enough? looks big enough to hold more than the amount of water that gets released, even if the diaphragm runs through middle of it.

If air & water comes out of the bleeders at the top of the system it's at positive pressure relative to the room pressure at those radiators. If nothing comes out it's likely to be at a negative pressure. With water in the system the bottom of the system is still at positive pressure from the standing column of water, but that doesn't mean it will be positively pressured at the top.

You desperately need to install a pressure gauge on the system, otherwise you're just flying blind. Just cranking the auto-fill valve a few turns one way or the other tells you nothing. If there's grit in the valve seat of the auto-fill or it's eroded enough to be seeping, the pressure will rise over time and pop the pressure relief. If there is an isolating valve between the auto-fill and the potable supply, turn it off. (Hopefully it won't be seeping too.) If there is a boiler drain port with a hose fitting on it, you can monitor/check the system pressure with a $15 temporary pressure gauge.

The pressure should be set 0.433 x the vertical height from the gauge to the top of the highest radiator, + 3 psi to cover the pressure fluctuations while pumping. Pre-charge the air in diaphragm expansion tank to the system pressure -0 psi / +3 psi.

A coal boiler with a retrofit gas burner old enough to have voted for Dewey is well past retirement age. It's delivering AT BEST 65-70% efficiency, and could be less than 50%.

 

[Astro46]

Thanks for the responses.
Now I understand the notion of negative pressure in the closed system. Sounds like the system has never been at negative pressure.
I measure the vertical height from level of pressure gauge to top of highest 2nd fl radiator as 16' x .433 +3 = 10 psi. The existing, very old pressure gauge has been showing just over 10 after system has been off for several hours.

I have thought about getting the addon "temporary" pressure gauge, but am concerned about being able to shut the drain valve off again afterwards, or if the "temporary" gauge connection leaks. Replacing the drain valve would mean draining the whole system. Who knows what problem could develop from that. Is it even ok to leave the "temporary' gauge in place?

i charged the diaphragm expansion tank to 11 psi. It was at 8. Supposedly it was charged to 12# at factory. Do they lose pressure over time? should I increase it?

Curiously, I shut off the isolating valve , after emptying the gallon bucket that collects pressure relief water. the boiler pressure, which was a little over 10 seemed to drop to showing 8. out of curiosity, I reopened the isolating valve and heard water flowing through the reducing valve, full open it sounded like, for maybe 30 seconds before it started slowly closing. Isn't that weird? if water wasn't flowing before shutting valve why start after closing and reopening? the isolating valve is closed again. Pressure gauge shows 10#.

The reducing and pressure relief are new. I installed them a couple of weeks ago. With the idea of fixing the problem of water coming from pressure relief, that still exists, starting after replacing the pump bearing assembly, as I said in original post.

We talked about replacing the boiler, about 10yrs ago. after looking at cost savings (figuring 50% efficiency for current boiler) vs cost of new boiler installation, payback was going to take the entire length of stated life of new boiler. Gas is currently cheaper, and likely new boiler installation would cost more. Since the existing system has had no problems (until I replaced the bearing assembly a couple of months ago) I chose to forgo a new boiler.

I am interested to your responses.

 

[Dana]

Yes expansion tanks change pressure over time- schraeder valves can leak ever so slightly. (Do your car tires ever need topping up?) If it leaks down fast, replace the valve, not the tank.

How much do you spend on gas over the course of a year?

The jacket insulation on antique boilers is usually de minimus or even non-existent. Is the boiler room the warmest place in the building during the heating season? It shouldn't be, and you're paying for that heat. If the boiler room is in an uninsulated basement most of that jacket-loss heat is going to heat up the great outdoors, not the floor above.

As a DIY installing a new modulating condensing boiler like the Westinghouse WBRUNG 080W or HTP's UFT-080W (same boiler under the paint- different support network) with a stainless fire-tube heat exchanger can cost about $2500. (Since it can use plastic venting, a mod-con is usually cheaper to install than an equivalent sized mid-efficiency cast iron boiler.) Running a mod-con boiler under outdoor reset control you can usually just replace the high volume pump with a lower volume higher efficiency version for about $200.

For yuks, take some of last winter's gas bills (or perhaps your next gas bill) and run a fuel-use heat load calculation on it with a presumptive 70% efficiency on the boiler. The existing burner is probably 3-5x oversized for your actual load, but this would put an upper bound on how much boiler it takes to actually heat the place.

When you turned off the isolating valve the system was hot. When you reopened it the system had cooled a bit, lowering the system pressure. But if it was only a few minutes apart it should not have been a high flow for 30 seconds.

Set your system pressure to 12=13psi- if it drops lower than 10 psi the boiler can experience flash-boil aka "kettling" on the heat exchangers, often with an audible sizzle, or even pops & bangs. With the tank isolated from the system pressure, pump it up to 15-16 psi.

 

[Astro46]

I'll get to looking at previous gas bills and checking the fuel-use heat load calculation in the next few days.

The system had already been off for a couple of hours when I shut and reopened the isolating valve. Hard to imagine it could have cooled that much in a few minutes. but who knows?

Is the idea here that putting more pressure in the tank will fix the pressure release situation. I noticed this evening that the boiler pressure gauge read (i know, old and maybe no accurate. would be a week before a temporary one would be available through home depot. Would it be ok to leave a temporary one in place?) just under 30#, with pressure release dribbling water. Isolation valve still shut off. this is what I am trying remedy.

btw: I did feel the boiler outer skin. Cool to touch, except in a couple of spots. There is an inner and outer sheet metal skin, packed with fiber glass (?) in between. The cast iron pipes running along basement ceiling is enough to warm things a bit. Though the basement isn't as warm as the apartments. I wouldn't say the boiler has heat exchangers. looks like a big burner with a concrete disc over it to diffuse the heat, and a pipe running through the middle. I can send pics if anyone is interested.

 

[Jadnashua]

Most residential boiler safety valves are 30psi and should start to open if the pressure reaches that value. Since they aren't really designed to be opened regularly, after a lot of use, they sometimes fail to seal.

ON a bladder type ET, make sure to tighten up the cap. Also, not all caps are created equal. SOme have a better gasket in them that helps to seal against leaks. In reality, the cap is the main seal, not the valve underneath.

 

[Dana]

I wouldn't say the boiler has heat exchangers. looks like a big burner with a concrete disc over it to diffuse the heat, and a pipe running through the middle. I can send pics if anyone is interested.

Of course the boiler has heat exchanger, between the fire-side of the burner chamber and the water side that is taking the heat out and distributing it to the radiators. In almost all cast iron boiler since the very beginning the heat exchangers are cast iron plates with water in them, between which the flame/exhaust flows, usually with a grid of pins / bumps on both the water & fire sides to increase surface area and turbulence to improve the heat transfer efficiency. With use & age those bumps get worn / corroded down over time, reducing the heat transfer efficiency, thus inevitably reducing the overall efficiency of the boiler. A 90+ year old boiler might have been 75-80% raw combustion efficiency when new, but it's nowhere near that mark now, especially when using burners & fuels it wasn't orginally designed for.

 

[Astro46]

thanks for that pic and explanation of boiler heat exchange opeation. Upon closer inspection I now see the exchangers. I don't remember why I got the idea that it had only a pipe running through.

 

[Astro46]

i closed the cold water feed valve a few days ago (it was never kept closed during operation in the past) to see what effect that might have. The Bell and Gossett instructions that came with the new reducer and pressure relief valves talked several times about how that valve should be kept closed after system was filled.

Seems that the result of this was that pressure relief continued to put out water (remember, this is a two story, 2 apt, 13 rad bldg, to give a vague idea of capacity), maybe 1/4/-1/2 gal/ day for a couple ofdays, then nothing. On the bad side, when I checked for air from radiator bleeder valves (system was off for several hours), there was none! so I opened the cold water feed valve and increased pressure on the reducing valve to being turned counter clockwise, (reduce system pressure) 1: 360 deg turn. Water came from bleeders, and now comes from the pressure relief. About a gallon in 12 hours.

I am starting to wonder if maybe the expansion tank is not large enough. I installed it when the original, built into ceiling developed a leak. it was much larger than the newer diaphragm tank. I was advised on which tank to install by the local heating and plumbing supply, in a neighborhood filled with brick 2 flats like mine.

the most confusing thing about all of this is that the system worked fine for the last several years, since I installed the diaphragm expansion tank and reduced the pressure on on the reducing valve to 2 turns out (counter clockwise). Bleeders all bled, no water from pressure relief (with old expansion tank and yearly service by local heating contractor the pressure relief always was letting water out), radiators all got hot. Then I had to replace the B&G series 100 bearing housing in october. and that's when the water from pressure relief started. as mentioned I have now also replaced the reducing and pressure relief valves, and increased diaphragm pressure to 16#. I don't understand why this started happening. or what will stop it.

 

[Jadnashua]

You need to calculate the actual volume of your heating system's water in order to know what size ET is required. The calculators rely on knowing that and the normal working temperature of your system to determine how much expansion there will be.

If there was a leak with the old parts, and the new ones tightened the system up, the expansion becomes more critical.

Many autofill valves can tend to leak a little as they age.

 

[Dana]

Unless you pre-charge the expansion tank to the new, higher pressure after adjusting up the auto fill to be able to bleed the top floor rads there is no way to know if it has sufficient expansion space to work with.

If it worked previously, it probably will again (if it's not leaking), but flying blind without a reasonably calibrated pressure gauge to compare against a reasonably calibrated AIR pressure gauge you're kinda screwed. It's like playing the board game "Battleship", with the only feedback being whether the pressure relief valve gives up.

In the spirit of continuing to stab in the dark, you could try lowering the high temperature limit by 10-20F to lower the peak presssure. Most systems set to 180F will still heat the place at a high-limit of 160F, or even 140F. As long as the returning water from radiation is at least 130F there is zero chance of condensation forming on the heat exchanger plates, accelerating corrosion. It's unlikely that this beast could even condense much with 110F return water given the likely condition of the heat exchanger plates.

Seriously consider replacing it with a cheap fire-tube modulating condensing boiler before the next heating season. For very high volume systems you might still need that monster B & G pump and plumb the mod-con primary/secondary, but in most 2-apartment systems it would be do-able pumped direct (no secondary loop) with a much smaller ECM drive pump when the boiler is operated under outdoor reset control. It'll probably cut the total fuel use by about half, and the pumping electricity use by about 80-90%.

 

[Astro46]

I have installed a pressure gauge on the drain valve (flushed valve to remove sediment before installing). It reads the same as the ancient pressure valve on boiler. pressure was reading 11# with system off for 4 hours. water coming from bleed valves on 2nd fl.

I removed the expansion tank and set its pressure at 11#.
Heat came on about 1 hr ago. boiler water temp climbed to 125 deg, (still continuing to go up), and pressure relief opened with water pressure at 30#. Put out 1/2 gal water, and for time being pressure relief and stopped putting out.

I have noticed that every time I have removed the diaphragm expansion tank to check its pressure, i get maybe 1/2 cup of water, including the water from about 14" of 1/2" pipe going to shutoff valve. The pipe to expansion tank comes from the check valve located in pipe at top of boiler. I've wondered about the seeming small amount of water when removing it. Is that normal?

heat is still on, temp continuing to rise in boiler (set for 180 deg). I'll see if more comes out later, as water temp goes up.

 

[Astro46]

water temp up to 145, pressure still at 30#, and 1 gal bucket under pressure relief overflowed a while ago, more still coming out.

 

[Dana]

Does the air pressure rise on the expansion tank as it heats up too? It should. If it doesn't the tank is isolated from the system by a valve somewhere. There shouldn't be a check valve between the tank and the system. There may be an isolating ball valve or gate valve, but be sure it's open before firing the system.

If the tank pressure rises in sync with the system pressure and it's blowing the pressure relief the tank is undersized for the system's water volume.

If the tank its undersized it might still be made to work. To give it a bit more room to expand into, don't set the tank to 11 psi, set it to 20 psi. The system pressure will rise pretty quickly to 2opsi then rise more slowly. Also, Lower the high-limit temperature by at least 10F, 15F is even better. Every degree it rises increases the pressure. eg: If the high limit is currently set to 180F, drop it to 165F, but leave the low-limit setting alone. If it doesn't have a separate low-limit aquastat but runs off a differential temperature, set the differential to something lower, no more than 10F.

Some pictures of the near-boiler plumbing and near-tank plumbing might help here.

 

[Astro46]

Does the air pressure rise on the expansion tank as it heats up too? It should. If it doesn't the tank is isolated from the system by a valve somewhere. There shouldn't be a check valve between the tank and the system. There may be an isolating ball valve or gate valve, but be sure it's open before firing the system.

If the tank pressure rises in sync with the system pressure and it's blowing the pressure relief the tank is undersized for the system's water volume.

If the tank its undersized it might still be made to work. To give it a bit more room to expand into, don't set the tank to 11 psi, set it to 20 psi. The system pressure will rise pretty quickly to 2opsi then rise more slowly. Also, Lower the high-limit temperature by at least 10F, 15F is even better. Every degree it rises increases the pressure. eg: If the high limit is currently set to 180F, drop it to 165F, but leave the low-limit setting alone. If it doesn't have a separate low-limit aquastat but runs off a differential temperature, set the differential to something lower, no more than 10F.

Some pictures of the near-boiler plumbing and near-tank plumbing might help here.

Dana, thanks for the advice. Friday night I removed expansion tank from system and increased pressure to 20psi. I turned boiler high temp from 180 to 165. I don't see any other temp setting (ie low temp). There is an 'altitude' gauge below the temp gauge. I was hopeful when on sat, there was no water released from system. On Sun. however it was back to previous situation, with over a gal released in morning when temp had to be brought from overnight 65 to daytime 69. No water release rest of day, I guess because system didn't need to run for long to maintain temp. Same story this (Monday) morning. while the system was running, and releasing water, the boiler temp read 145 deg, boiler pressure was just over 30# and expansion tank pressure showed 28#.

I can understand that perhaps expansion tank is too small, but can't understand how it all worked for several years, until I replaced the bearing housing. at that time I shut off the return valves, cold water feed valve, and water drained from between the pump and check valve when I pulled out the bearing assembly. Then I turned it all back on.

There should be 5 pics below. As the poster, it seems, I can't see them, so let me know if you can't and I'll find another way to post them.

 

[Dana]

It sounds like something is blocking the pipe between the system and expansion tank, something that may close up at some temperature (?).

If you can't control the differential temperature between high-limit and low-limit the pressure change is going to be about the same if the temperature rise between idle and full-hot is the same.

This boiler isn't worth spending a lot of time adding retrofit controls to deal with it. If there's another location where a second expansion tank can be added that might be an OK stop gap solution to get you through the winter. But yarding the whole thing out and starting over with a right-sized boiler and right-sized expansion tank is really the "right" thing to do. After 92-93 years thing has gone through 3-4 boiler-lifecycles worth, and isn't really worth fixing.

 

[Astro46]

I had wondered if pipe to expansion tank is blocked, so opened the tank isolation valve when it was off. Water flowed. But if the blockage is temp related, then of course that is different. Just wondering, what makes you think it is a temperature related blockage?

I have tried inserting the images in a different way. If want to click on the images they appear larger and have labels, which can't be seen in the small pics.

 

[Reach4]

I have tried inserting the images in a different way. If want to click on the images they appear larger and have labels, which can't be seen in the small pics.

That is quite the cradle for the expansion tank.