Replaced Expansion Tank, still leaking (just a little)

[AnthonyD]

Hello,


Thank you for taking the time to read this. Hopefully someone will be able to shed some light on my current situation/


I recently woke up to a wet carpet in the living room. After some research, I realized the overflow valve on my Crown Boiler was leaking. I put a painter’s bucket (5 gallon?) a and the next day it was almost a ¼ full. It woud just trickle but them when the heat kicked on, the psi went over 30 and it would drain out pretty fast. I replaced the expansion tank and that seemed to fix the problem but not fully. It is about 95% better but it is still SLOWLY leaking out. I put the bucket under it and in the past two days maybe 1 ½ cup has come out. Not enough to completely cover the bottom of the bucket, but still, it is still leaking. It seems the PSI is still going up to about 30 at times. I tired to let out some of the water (pressure) when it got that high but that does not seem to have done anything. I am happy with the result of replacing the expansion tank but I want it so it doesn’t leak at all.


Anyone have any thoughts or tips on what to do?


Thank you very much

Ant

 

[Reach4]

I am happy with the result of replacing the expansion tank but I want it so it doesn’t leak at all.


Anyone have any thoughts or tips on what to do?

What did you set the air precharge to? What are the specs for your system regarding pressures, temperatures and gallons? How big is your new expansion tank? I won't be able to interpret your numbers into an action item, but having the numbers available to a knowledgeable person could help him make a recommendation.

 

[Sponsor]

 

[AnthonyD]

What did you set the air precharge to? What are the specs for your system regarding pressures, temperatures and gallons? How big is your new expansion tank? I won't be able to interpret your numbers into an action item, but having the numbers available to a knowledgeable person could help him make a recommendation.

Hello,
The new expansion tank i use was an extrol EX -30. I was told it was pre-charge to 12 PSI and was told from the guy at the plumbing store that i did not need to inflate it.
I honestly could not answer "What are the specs for your system regarding pressures, temperatures and gallons?" . If you can help me determine this information, i would be happy to do so. It is a pretty big boiler (i am guessing). It is setup on 3 zones with a 4th not in use. The boiler does not have a model number so not too sure how to find that out.

The expansion tank is the same size as the one that was there (bout the size of a propane tank, maybe just a tad smaller).

The old tank is a gray tank: it says HXT-30 (12 PSI-precharge, 5 gallon,. max pressure 115). I never had any problems with overflow leaking with the old tank for 5+ years.

 

[Reach4]

What is the lowest that the pressure gauge reads when the system is not heating?

 

[AnthonyD]

What is the lowest that the pressure gauge reads when the system is not heating?

i will double check this evening when i am in-front of it, but when i last looked, it was about 20. I shut off all themostats tonight, give it about 15 minutes, and get a more accurate reading..but off hand, 20

 

[Jadnashua]

You need to verify the pre-charge on the expansion tank. IF it is properly sized and pre-charged, and the system pressure is still rising, then one of two other things could be wrong that I'm aware of:
- your autofill valve is leaking and over pressurizing the boiler loop
- if you have either an in-tank hot water coil or an indirect WH, there's a leak between the heating loop and the potable water.

To properly size an expansion tank, you need to know three things and can use the defaults on the others:
- how much water is in your heating system
- the low temperature set point
- the high pressure set point

Determining how much water is in the system takes some measuring the length of the pipes and reading the specs on the boiler and radiators. Once you have those numbers, you'd plug them into a calculator, and it would tell you the size you need. There's a free one at:

http://www.watts.com/pages/support/sizing_ET.asp

Once the safety pressure relief valve has been opened a bunch of times, sometimes, it doesn't seal well. But since your pressure is rising to 30psi, and it's opening, it's probably okay. If it constantly leaked when the pressure was lower, it would be time to replace.

 

[AnthonyD]

You need to verify the pre-charge on the expansion tank. IF it is properly sized and pre-charged, and the system pressure is still rising, then one of two other things could be wrong that I'm aware of:
- your autofill valve is leaking and over pressurizing the boiler loop
- if you have either an in-tank hot water coil or an indirect WH, there's a leak between the heating loop and the potable water.

To properly size an expansion tank, you need to know three things and can use the defaults on the others:
- how much water is in your heating system
- the low temperature set point
- the high pressure set point

Determining how much water is in the system takes some measuring the length of the pipes and reading the specs on the boiler and radiators. Once you have those numbers, you'd plug them into a calculator, and it would tell you the size you need. There's a free one at:

http://www.watts.com/pages/support/sizing_ET.asp

Once the safety pressure relief valve has been opened a bunch of times, sometimes, it doesn't seal well. But since your pressure is rising to 30psi, and it's opening, it's probably okay. If it constantly leaked when the pressure was lower, it would be time to replace.

Thanks Jad. , quick follow up question to start. would you be able to elaborate on how i can verfi ythe pre-charge. Can i just connect a tire pressure gauge to the tank to get the reading? If so, (i would think), I Should do this when the boiler is off.

 

[Dana]

The pre-charge has to be tested with the water side of the expansion tank at atmospheric pressure. If you're lucky there are valves for isolating the tank from the system and a valve for de-pressurizing the tank (or you can partially disconnect it to relieve the pressure.) You shouldn't get a huge amount of water out of the thing unless it was very under-charged initially. A cup or two maybe, not a gallon or two.

 

[Jadnashua]

For an expansion tank to work, it must first be intact, then, it must be sized properly for the system so that the bladder in it is not stressed beyond it's design, then, to start with the bladder at the proper position, it must be precharged to the normal system pressure. This means that, once you do apply the system water pressure, the bladder will be in the right position with enough available movement to work properly. When they fail, the bladder usually ends up with a leak in it and less common, the tank rusts out. This allows all of the air to leak out and the tank can no longer perform its function. If when you attempt to add air, you get water out, the tank has failed. If it's dry, but the tank seems heavy, the air pressure may be way too low, and the tank is full of water. Under normal circumstances, it's mostly empty until it needs to accept some expanding water during a heating cycle. When things cool off again, it contracts, and the bladder will push out the excess fluid, maintaining the system pressure. If you tap on it, and it is heavy or you hear a thud verses it ringing, something's wrong.

The bladder in the tank is similar to a tire, so yes, you can just use your air pressure gauge to check it, but as has been said, that will only be accurate if there's no water pressing on the other side and the bladder can expand and that cannot happen if the water side of it is not open to the atmosphere so the fluid can be pushed out. Once precharged properly and the system is working, the air pressure in the tank will be the same as the system water pressure, and is a place you can use to check any pressure gauges in your system.