Increasing Pressure in Gravity Hot Water System

Bruce_10

Just when I thought I figured out what was going on, I seem to be right back where I started.

Midday today while the system was cool, I opened the lower drain and got some small amount of water then a very slow, drop, drop ,drop into the bucket. I went to the highest radiator in the system and opened the bleed valve. The flow at the boiler became a mighty gush and air was pulled into the radiator. I drained some water and closed the lower drain. Then closed the radiator bleed valve. Then, slowly the pressure in the system built up again. Opening the radiator bleed valve released air, then eventually water. The pressure would then build again (over the period of 20 to 30 minutes) and I continued to bleed a few times an hour over several hours always getting about four ounces of water at a time before the flow became slow drops.

I finally had to start the system back up for some heat. The boiler gauge did exactly what it has been doing...going beyond the highest reading while the gas burner is on.

My latest theory is that the expansion tank does have some water and pressurized air in it and the connection between it and the system is very restricted so it takes minutes to push water back down (and thereby rebuild the pressure in the system). Does this make sense?

We did get up on the roof this afternoon and were able to push a coat hanger in to the exhaust pipe of the expansion tank. It would not go around the 90-degree angle and down into the tank however. When it started snowing again, I got off the roof. Should I go back out there and see if I can
get something to go around that bend and into the tank?

This is frustrating and fascinating. Any more insights on the mystery are welcomed.

Bruce_10

Question about increased pressure

I have a gravity hot water heating system circa 1916
(coverted from coal to gas circa late 1960's)
in my house which as worked very well in the six
years I've owned the house. I even moved a radiator
and added a kickspace heater in the remodeled kitchen.
Lately when the boiler kicks on the pressure gauge (reading in feet) climbs well above the highest reading (70 feet)
which it didn't do before. Then when the burner cuts out
by the water temp sensor it drops down to 10 feet (normal
cold reading is 23 feet). I presume there is "friction"
in the piping buidling up. Is there some recommended procedure (additives? processes?) to drain and "clean"
the piping/radiators? Websites? Any help would be appreciated.

Dave_12

Expansion Tank

You need to check the expansion tank (if there is one). Is the tank in the attic, with a blocked line? A waterlogged compression tank in the rafters? Or a broken bladder type?

Look for that first before you go looking to clean pipes. Also does the system have a pump or is it still gravity?

Brant Wininger
Cody Sales & Engineering

Bruce_10

re: expansion tank

Thanks for the insight. The system is still gravity.
After finding this website and reading about gravity systems I am looking into replacing this relic boiler with
a new one and moving to a closed, pumped system. I
am trying to get through the rest of this heating season first. (I live in Denver and it is snowing today so our heating season is far from over) The system was drained 5 years ago when the modifications were done. No other
servicing since then. The expansion tank is in the attic, and there is an overflow pipe on the roof. So I assume
that it is the "open" system original unit.
I haven't seen any water come out of it. I'll get up
in the attic this weekend and check out the expansion tank.

If it wouldn't hurt to "flush" the system I thought I'd
actually fill it up enough to make the expansion tank
overflow onto the roof and then drain the entire system and refill it. I will also clean the heat exchanger in the boiler with the wire brush tool that is still hanging on the wall of the basement. I am still amazed that this boiler works at all. I can't even fathom it's "efficiency".


They system took a long time to stabilize after the modifications due to trapped air, but for the last three
winters it has been quiet and stable (hardly any water
needed). This higher and higher pressure reading has
been happening since mid winter this year.

Dave_12

Definately check the overflow on the roof. You may have a time bomb waiting there. You also should get a relief valve on the system.

Bruce_10

follow up

I will check on the tank and make sure the overflow pipe is not
blocked by something. If the weather turns reasonable this
weekend I may drain the system. Another homeowner here
in Denver with a similar system told me I am supposed to drain
the system in the summer and leave it dry out for a month or so.
Seems to me that that would invite more corrosion over the long run.

The boiler does have a relief valve (a pecuilar black block on a pivot)
on one supply line coming out of the top of the boiler. I have no
idea what pressure would trigger it. I may look at it closely
and see if there are any markings on it this weekend as well.

Thanks again

Steamhead

Bruce, I agree you may have a time bomb there

It's possible that the old tank in the attic was disconnected long ago and just left there. If there's no water in that tank but the pressure is skyrocketing it can't still be connected. There may be another tank in the basement ceiling. Or there may not be a tank, in which case you need to have one installed as well as replacing the relief valve.

As a temporary fix, you may want to open the drain on the system, open the bleed on one radiator in a room you don't use much, and drain enough water from the system to fill that radiator with air. This will take up some of the water's expansion- keep an eye on that gauge to make sure it's enough.

The "black block on a pivot" sounds like an old damper regulator used with coal firing. Post a pic of this unit and we can tell you for sure.

Have a pro look at this system. Try the Find a Professional page of this site to locate one near you.

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Bruce_10

More Developments and pictures

Thanks for all of your help on this. You guys are great.
I have taken some pictures of the beast. I think Steamhead may be right
and the cap with the pivot on the top of the right hand
supply stack may have been connected to the flue damper
a long time ago. The close up picture of that cap is labeled "valve"

We did go up in the attic today and there is a old expansion tank
up there. It "sounds" empty. While there were fittings for a tank level
tube, they were plugged. This was probably original
since no one can get in the attic routinely. You have to crawl through
a small openning in a closet to get up there and then crawl
on your belly to get around. There are no signs of the tank being disconnected and no area of the ceiling or wall near it show any signs of being repaired if the disconnection was done from below. There is NO other expansion tank in the system. I have looked all over the basement ceiling.

The "altitude" gauge stays at 23 feet (where it is in the picture) until
the gas burner comes on. After a few minutes of heating the gauge goes above 70 and stays there until the burner cuts out from the Honeywell temp. cut-off in the left supply stack. (I've lowered that cut-off temp to 140 degrees for now). Then the "altitude" drops to 9 or 10. This cycle repeats until the house thermostat stops calling for heat. In past years, the gauge would go up to about 50 and would drop to around 16. The thermometer in on the boiler does not work so I don't know the "local" temperature. I am assuming the Honeywell cut off setting is close to the correct temperature. The radiators get to about 130 degrees right now.

When the system was cold this afternoon I opened the drain on the return line. Only a bit (a quart or so) of water came out and the altitude gauge went
to zero. I closed the valve and added a small amount of water to bring the gauge back to 23 feet. This means
to me that the expansion tank is either disconnected or is no longer
open to the atmosphere. It was snowing so I couldn't go on the roof and check the line out from the expansion tank. The system is working, in that all radiators get hot (about 130 degrees). But the circulation must be awfully
slow. (It takes 30 minutes for the radiators to begin to feel warm).

I will open a radiator on the upper floor tomorrow and see if I can drain
the system down some and provide some air space as Steamhead suggested.

I am having a professional (Advanced Hydronics) come on this
Tuesday to talk about replacing the boiler and adding heat to part of the basement and to an unheated second floor "sleeping porch" this summer. But I still have to get through the next few weeks with the current system.
I guess I should feel lucky that a system Patented in 1904 is still
heating my house (for now). I hope its last few weeks will be safe ones.
Thanks again guys.

Steamhead

That's a \"snowman\" boiler

one of the least efficient types of boiler. One of my Dead Men's Books says this type of boiler cannot be expected to show more than about 40% efficiency on oil. This should hold true for gas also. It's obvious why the thing has to run 30 minutes before you get heat. Replacing this boiler with one sized to the house's heat loss could cut your fuel consumption in half.

The device in the "valve" photo is definitely an old damper regulator. It worked like a beam balance with adjustable weights. The "beam" and weights have been removed.

Your observation on the results of draining the boiler is dead-on. You might try to find where the pipe came down from the attic tank to connect to the system, to see if it's still hooked up.

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Bruce_10

check on connections.

> one of the least efficient types of boiler. One

> of my Dead Men's Books says this type of boiler

> cannot be expected to show more than about 40%

> efficiency on oil. This should hold true for gas

> also. It's obvious why the thing has to run 30

> minutes before you get heat. Replacing this

> boiler with one sized to the house's heat loss

> could cut your fuel consumption in half.

>

> The

> device in the "valve" photo is definitely an old

> damper regulator. It worked like a beam balance

> with adjustable weights. The "beam" and weights

> have been removed.

>

> Your observation on the

> results of draining the boiler is dead-on. You

> might try to find where the pipe came down from

> the attic tank to connect to the system, to see

> if it's still hooked up.

>

> _A

> HREF="http://www.heatinghelp.com/getListed.cfm?id=

> 157&Step=30"_To Learn More About This

> Professional, Click Here to Visit Their Ad in

> "Find A Professional"_/A_

Bruce_10

check on connections

I suspect that expansion tank is plumbed off of the supply line that runs to a radiator just below it on the second floor. (See attached sketch). I have very carefully examined the two walls and the ceiling above that radiator to see if any re-plastering has been done which would indicate some work on the system piping. No sign of any. That radiator works as well as any other in the system so it is getting hot water through it.

And yes, I agree that it is time to move from 100+ year-old technology
to the more modern world for efficiency purposes. At least part of the
60 percent loss heats the basement and the kitchen right above the old beast.

The morning heat cycle is still underway. Once the system shuts down and cools I'll drain that radiator below the tank and see what happens. When Denver's unusually wet weather ends (we seem to be stuck at 36 degrees and snow showers for days on end now), I'll get up on the roof and see about that line off the top of the expansion tank.

Now that I think I understand the system, I guess we'll make it till the end of May without a disaster. Thanks again for your insights.

Steamhead

Check the valve

in the pipe feeding water to the boiler. It's probably not shutting off all the way. If there is an automatic valve there it will need to be replaced, but you can turn off the manual valve in its supply. If it's just a manual valve it might be as simple as replacing the washer in the valve.

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Bruce_10

balancing act

Thanks again for the reply. I thought about the fill valve too. It is manual. I very carefully marked our city water meter (which has a dial that can read tenths of gallons) as I was bleeding the system and pressure was rebuilding. No movement of the meter at all. However, at four this morning while tossing in bed, it hit me that the radiator in my bedroom is the same height as the one I am putting air in across the hall. I am presuming that the line to the expansion tank is blocked. So what I have here is essentially a "closed system". When I let air into one radiator and seal the system back up again the water in the bedroom has water "above" the level in the one I just partially drained. That higher water should excert some pressure on the air in the partially drained radiator.

There are four radiators on the second floor. Two are 36 inches high (the one below the expansion tank and the one in my bedroom) one is 30 inches and the one in the bathroom is 20 inches. The one in the bathroom and the one below the expansion tank are on the same riser of the boiler. So I opened both of those bleed valves and drained the shorter radiator and put more air into the taller one. I didn't have enought time "level" the two before I had to get to work. So I closed them up and fired up the boiler while I was eating breakfast. The boiler gauge still went above "normal" but when the temp-cut out triggered the pressure was 60 ft (not above 70 ft. like before). So, I think I am finally on the right track here.

I did get a recommendation from someone about a local plumbing company that specializes in these old systems. I will call them today. Our weather is finally supposed to return to normal by the end of the week, so our heating season should just about be over.

Thanks again.