Still t-shooting ex-gravity FHW blowing off - more info

Brad White_9

plus it is a conventional air cushion type that can become water logged. Tap it and see, both when it is cool and presumably less full, and again when it is at full fire and pressure. See how much more full it is.

I would replace it with a series of bladder tanks and eliminate that variable. Short money, really.

Daniel Nolan

Pressure is building....

Still having trouble with my gravity FHW system that has been converted with a circulator. It blows off pressure and about 1-2 gallons of water per day.

So far I have shut off the water feed before the infeed valve, and observed the following:

Pressure starts at 12 psi, temp set at 140 / 160

amount of blowoff is reduced with infeed shut off, seems like maybe just one time it blows off.

when system comes on after long wait (during the day it's on a low setting, then at 5pm the setting is higher) a churning sound is heard for 5 - 10 sec, sounds like air in the pipes (I believe the circulator comes on right away)

As the system cycles, the pressure gradually builds. After 2 cycles it is over 20 psi. When the circulator comes on the pressure goes up a few psi. If it cycles enough times, the pressure will build high enough for it to blow off when the circulator comes on (pressure is near 30 psi)

I believe that what happens is that when the system cycles enough times it builds up pressure and blows off some water. Then when it is not running the pressure drops back down. With the infeed off I have observed the pressure down to almost zero after 1 day and some blowoff.

I have bled all but 1 of my radiators several times. The last one gets hot so I do not suspect that it has any significant amount of air in it. Can't get to the bleeder - long story - but I was able to bleed this one by loosening the joint at the top pipe (return?).

I should also note that we drained the system early last year to remove one of the radiators on the first floor. When we remodeled the kitchen, we took out the radiator to make room for cabinets. This one was the smallest of the 4 on the first floor by far. Since we took the wall down between the kitchen and the living / dining room there was little concern about replacing the heating in that area right away. We wanted to see what the winter would bring and either do radiant or a kickspace depending on need. The connection in the basement was already 1" copper connecting to the large black feed & return (2 or 3") so we just cut off the pipes about 3 feet from the connection to the F&R and put ball valves on. The plan was to be able to make future connections without draining the whole system.

Some questions:
Do I have trapped air somewhere? How can I bleed this out? Can I add some sort of device that will help get the air out? Is it possible that some part of the system is blocked? (all radiators seem to get hot) How badly did we mess up the system by removing that radiator? Would simply connecting the F&R on the kitchen loop help? What are my next troubleshooting steps?

Thanks in advance for any tips. Seems like owning this old place is always a challenge.

-Dan

Brad White_9

Still thinking

that it is an under-sized expansion tank or tanks, Dan.

The fact that pressure goes up when heated leads me to this. I do not see that you have trapped air (you might but that acts like an expansion tank in a way). In short I see that as a secondary issue.

How big again was the expansion tank? Was it conventional air cushion type or a diaphragm type?

As Ed says below, if conventional, it could be water-logged. Then it ceases to be an expansion cushion...

Normally I install a series of #30's because they are inexpensive and can be added for little money. I have put as many as four on some GHW systems. And the higher they are in the system the more effective they are.

Big Ed

Expansion

The expansion needs to be fully drained.

CHARLES_4

Nowhere do you mention an expansion/cushion tank. Is there one? If not, stop bleeding the radiators. Air is your friend in this system, if you know where it is. In this case, you want it at the top of your highest/tallest radiator. You can't compress a liquid; that's why you need an air pocket. As the system heats, the air pocket(s) will compress and heat most of the radiator(s) with the air space. The reduced water capacity will not diminish your heating capacity signifcantly. Of course you will eventually need to address the cushion tank issue...

Mike T., Swampeast MO

Two General Causes...

...of excessive pressure in a hot water system.

Either 1) water at high pressure is entering the system or 2) there is no space for the water to expand as it heats.

Common causes of 1)

a) Improperly adjusted or defective feed valve. If you have an auto feed valve, shut off the hand valve either before or after the device. If problem goes away attempt re-adjustment or repair. Replace if both fail.

b) Leaking domestic hot water component. This can be from either a "tankless" coil or indirect tank. Isolate the house pressure from the system--if problem goes away then you can fairly assume a leak. If your boiler doesn't provide DHW then, obviously, this can't be a possibility.

Common causes of 2)

In your case (a gravity conversion that was working properly before), the number one suspect is the compression tank. (I do presume that you have a compression tank near the boiler and that the old open expansion tank--usually in the attic--has been removed or cut off and abandoned).

If this is an old, plain tank (it will be quite large) there will be one connection at the bottom (leading to the boiler) and one at one end (for draining). In normal operation the tank should be about half filled with water. If it has become filled with water it is called "waterlogged" and there is no longer a cushion of air to allow expansion of the heating water.

Look for a valve on the pipe leading to the tank. If you find one, make certain it is FULLY open (the handle is frequently removed to prevent inadvertent operation). If it's closed, you've found the problem--but the tank may still be waterlogged.

The solution to a waterlogged tank is a drain and re-fill. Completely drain the system AND the expansion tank. Sometimes there's a draincock on the tank--other times you must remove a plug.

To re-fill, close the tank drain connection and also close the valve leading to the tank (if one is present). Fill and bleed the radiators. Since you installed ball valves at the old rad connections, bleed them as well. Open the valve to the tank (if applicable). Then operate the system.

Have you eliminated these possibilities?

Brad White_9

Listen to Mike

If not one of the more detailed factors he listed, it is a miracle, the Will of Allah and should not be messed with. You may have to move

Mike T., Swampeast MO

Another simple cause:

If there is not automatic fill device, the manual fill valve may have a slight leak.

Daniel Nolan

More info yet...

> ...of excessive pressure in a hot water

> system.

>

> Either 1) water at high pressure is

> entering the system or 2) there is no space for

> the water to expand as it heats.

>

> Common causes

> of 1)

>

> a) Improperly adjusted or defective

> feed valve. If you have an auto feed valve, shut

> off the hand valve either before or after the

> device. If problem goes away attempt

> re-adjustment or repair. Replace if both

> fail.

>

> b) Leaking domestic hot water

> component. This can be from either a "tankless"

> coil or indirect tank. Isolate the house

> pressure from the system--if problem goes away

> then you can fairly assume a leak. If your

> boiler doesn't provide DHW then, obviously, this

> can't be a possibility.

>

> Common causes of

> 2)

>

> In your case (a gravity conversion that was

> working properly before), the number one suspect

> is the compression tank. (I do presume that you

> have a compression tank near the boiler and that

> the old open expansion tank--usually in the

> attic--has been removed or cut off and

> abandoned).

>

> If this is an old, plain tank (it

> will be quite large) there will be one connection

> at the bottom (leading to the boiler) and one at

> one end (for draining). In normal operation the

> tank should be about half filled with water. If

> it has become filled with water it is called

> "waterlogged" and there is no longer a cushion of

> air to allow expansion of the heating

> water.

>

> Look for a valve on the pipe leading to

> the tank. If you find one, make certain it is

> FULLY open (the handle is frequently removed to

> prevent inadvertent operation). If it's closed,

> you've found the problem--but the tank may still

> be waterlogged.

>

> The solution to a waterlogged

> tank is a drain and re-fill. Completely drain

> the system AND the expansion tank. Sometimes

> there's a draincock on the tank--other times you

> must remove a plug.

>

> To re-fill, close the tank

> drain connection and also close the valve leading

> to the tank (if one is present). Fill and bleed

> the radiators. Since you installed ball valves

> at the old rad connections, bleed them as well.

> Open the valve to the tank (if applicable). Then

> operate the system.

>

> Have you eliminated these

> possibilities?

Daniel Nolan

More info yet...

Some further detail, refer to above post.

1a - I suspected the auto feed valve so I have run the system with the main feed shut off. Blowoff is dramatically reduced, but I think maybe there is another issue that causes the pressure to build, blowoff, then cooling and the system pressure goes back down and calls for more water. With the main feed off the pressure has dropped to zero on a few occasions. (I have refilled and shut the main off again afterwards)

1b - Yes it is tankless, but zero pressure in the system at any time should tell me that there is no leak in that loop. I feared this for a while, but unless there is an occasional leak (which seems impossible) this should not be the issue.

2a - Yes, I have a large compression tank in the rafters above the boiler. Probably 12" dia by 3' long. No tank in the attic.

2b - Connections to boiler as stated. Unsure of level of fill.

2c - Yup, valve on pipe from boiler to tank. It is open all the way. Also a large Taco valve there at the connection to the feed on top of the boiler.

2d - I have closed the valve on the piping to the tank, and opened the drain valve (like a garden hose valve) on the bottom of the tank. Only got about a gallon of water out of there - will it just drain empty or do I have to vent it somehow? If there is only 1 gal in there do I have extra cushion or is that bad? Yes, I reopened the valve after I drained the tank.

2e - Bled the ball valves, but have not followed the sequence listed above.


What should I try next?

Thanks,
-Dan

Mike T., Swampeast MO

The boiler feed shut off valve may be leaking slightly.

I'm not familiar with tankess coils, but do suspect it could have an intermittant leak that only shows up during heating cycles as the metal expands. Can you not shut down the domestic portion temporarily?

Gravity systems can be very persnickety when it comes to filling. Whenever major work has been done, it seems best (by far) to do a complete drain and re-fill. And, no, such is never a fun job for anyone...

Ron Schroeder

Compression tank

You need to get air in to get all the water out, if your only getting out a gallon I suspect its not completely empty before you start recharging it. I would take Brads sujestion and add multiple bladder expansion tanks. IOf oyur still having problems sow us a picture of that tank and piping