Expansion tank or something else?

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Old 12-29-14, 06:32 AM
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Expansion tank or something else?

Been a lurker on here for a while, but finally decided to join. I have searched and read a few threads regarding the issue I am having. FiancÚ and I bought this house in July, and have had a leaky T&P valve ever since. Finally last night I went downstairs to try and see what is going on. It is a Viessmann boiler running 6 zones (1 is DHW (indirect)), single circulator, TACO controller, with Amtrol 30 tank. Everything supplied via a well.

1. I cranked the thermostat in our bedroom and ran downstairs. Water started circulating, and boiler fired after a minute or so. Boiler came up to temp and shut off (pressure stayed below 30psi), no water out of relief valve. Water continued to circulate, and boiler fired again, came up to temp, and this time pressure creeped above 30 psi and water dripped out the relief valve until pressure dropped below 30 psi. Now I have read the stickys and such, unfortunately I did not precisely note the pressure prior to the boiler firing the first time, but I can say it was around 15 psi or so which is normal (I will verify for sure and take some pictures of my system to post tonight).

2. I did the tap test (I know, not very accurate) on the expansion tank and the whole thing sounded like a "thud".

3. Depressed the valve on the bottom of the tank and got no water, but little to no air either, which is why I suspect the tank may be my issue. With no pressure in the expansion tank, the system could be "overfilled" correct, causing the over-pressurization?

4. I understand there could be a hole in the DHW coil causing over-pressurization that way, but if that was the case, wouldn't the system only over-pressurize when the boiler fires for DHW demand, or am I thinking of this wrong?


Like I said, I will do some more investigating tonight, and will post pictures of my setup to better help you guys help me.



Thanks for the help guys!
 
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  #2  
Old 12-29-14, 07:12 AM
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Either add air to the tank or replace it. Then set the system pressures/fill to 12-15 psi and see how it runs. With no air in the tank, it's not doing its job.
 
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Old 12-29-14, 07:25 AM
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Exactly what I am thinking. Since there doesn't appear to be any air in it at all, can I add air to it without first draining the system, or would it be good to drain the system anyway?

I have been doing a bunch of reading, and there doesn't seem to be much info on the tank being full of water without the bladder being failed i.e. no pressure in the bladder.
 

Last edited by NorthMaine; 12-29-14 at 08:08 AM.
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Old 12-29-14, 08:41 AM
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I did the tap test (I know, not very accurate)
No, not "not very accurate", but rather, not accurate at all.

I wish there were some way to put this internet superstition to rest...

With no pressure in the expansion tank, the system could be "overfilled" correct, causing the over-pressurization?
I suppose that you could say 'overfilled', but that's not exactly accurate... it means that there is no 'air cushion' for the expanded water to push into in order to control the pressure.

I understand there could be a hole in the DHW coil causing over-pressurization that way, but if that was the case, wouldn't the system only over-pressurize when the boiler fires for DHW demand, or am I thinking of this wrong?
A little bit wrong...

If there were a leak in the indirect from the domestic side to the boiler side, it would over pressurize the boiler ALL THE TIME. Not only when the DHW was calling for heat.

The same would be true if the PRESSURE REDUCING VALVE were leaking through internally.

Here's the bottom line:

If the boiler will sit and not leak the relief valve when there is no heat call, and the pressure remains stable at 12-15 PSI, then the indirect and the reducing valve are most likely fine.

If the relief valve ONLY weeps when the boiler is being heated, then 99.9% it's your expansion tank.

This, and the fact that you said there's no (or little) air in the tank means the first thing you need to do is correct that situation.

If you got no water from the air valve, the membrane MIGHT be intact, but still MIGHT be bad... so first try recharging the tank per the step by step instructions and monitor for a while. If the problem is fixed, then that's great... if it comes back, change the tank (and add the optional valves to the tank connection!)
 
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Old 12-29-14, 08:42 AM
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Read this sticky: http://www.doityourself.com/forum/bo...sion-tank.html

You don' t need to drain the system to check the air in the expansion tank, just depressurize the system.
 
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Old 12-29-14, 08:45 AM
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Now I have read the stickys and such,
I think he did Gil, but for future readers it's a good idea to add the link here...

And while we've got our hymnals open, might as well add link to this one also:

http://www.doityourself.com/forum/bo...ure-gauge.html

Because they go hand in hand...
 
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Old 12-29-14, 08:48 AM
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Thanks for the info. I read that sticky and will be checking it out tonight. I haven't really monitored it that closely before last night, but I am 90% sure that the pressure stays stable when not being heated.

Need to pickup a bicycle pump or the like on my way home from work tonight.
 
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Old 12-29-14, 08:51 AM
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I did read that yes, thanks NJ. When I said drain, I meant depressurize, sorry.

Thanks for the info!
 
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Old 12-29-14, 09:00 AM
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I don't know if this is any good or not, but if you've gotta buy a hand pump, you might consider this instead. Says it runs on 12 VDC and 120 VAC:

http://www.amazon.com/Black-Decker-A...tor+with+gauge

From what I can see, it looks like a decent bicycle pump will be at least half the price of this, and some are equal...

Never know when yer gonna need to pump a tire!
 
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Old 12-29-14, 09:03 AM
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Thanks. I have a 12v pump, but that don't do me much good in the basement haha. Also have a compressor, but I am not about to carry that down their either. I will probably just get a bike pump for like $15 or something. For what I will use it for, I think it will be fine.
 
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Old 12-29-14, 10:30 AM
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Please advise if this doesn't make sense or not. Attached is a diagram of what my system looks like. In order to isolate the tank and depressurize the system, my plan is as follows:

1. Shut cold water supply to boiler.

2. Shut all supply valves.

3. Shut all return valves.

4. Open boiler drain and drop boiler pressure to 0.

5. Pump up expansion tank.

6. Open cold water supply.

7. Open supply valves.

8. Open return valves.


Using the above, I don't think I should get any air in the system should I? In the event I do, how can I bleed it off or will it work its way out through the air bleeders throughout the system?

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  #12  
Old 12-29-14, 10:47 AM
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1. Shut cold water supply to boiler.

Yes, steps 1 and 2 below
2. Shut all supply valves.

3. Shut all return valves.

It really shouldn't be necessary to shut those valves.
4. Open boiler drain and drop boiler pressure to 0.

Yes, step 3 below
5. Pump up expansion tank.

Here you need to follow the step by step exactly. Steps 6, 7, and 8 below in particular. If you only pump the tank one time, you will NOT get all the water out of the tank.
6. Open cold water supply.

7. Open supply valves.

8. Open return valves.
You are starting with a tank that is full of water. The point of repeating the steps 6,7,8 below is to assure that ALL the water is pushed out of the tank. When you pressurize the tank to 12 PSI the first time, you will (SHOULD) see the boiler gauge ALSO go up to 12 PSI. This is telling you that there was water in the tank and some has moved out of the tank and back into the system.

When you again drop the boiler to zero, and repressurize the tank again, you will AGAIN see the boiler pressure rise...

By repeating this process several times, ALL the water in the tank will be pushed back into the system and the air pressure in the tank will be correct.

Only when the boiler stays at zero and the tank stays at 12 are you certain to have all the water out of the tank.

I don't think I should get any air in the system should I?
No, you should not introduce any air into the system with this procedure as long as the tank membrane is intact.

But then you said, and there's another step to add maybe...

how can I bleed it off or will it work its way out through the air bleeders throughout the system?
Are these 'air bleeders' the automatic float type? If so, there will be a cap on the top of each one that you should tightly CLOSE before you drop the pressure in the boiler because these CAN SUCK AIR into the system... and no, you don't want that...

This all probably sounds a lot more complicated than it really is... but it's really not... just go slow and follow the steps below TO THE LETTER and you will be fine.

-----------------------------------------------------------------------------

1. Shut off boiler and allow to cool to under 100░F.

2. Shut off water supply line to boiler.

2a: CLOSE TIGHTLY the caps on any 'automatic float type' air valves!

3. Drain only enough water from the boiler drain (note: this does not have to be THE boiler drain. It can be ANY drain valve on the system. Use the one that is most likely to be able to not leak when closed again!) to drop the system pressure to ZERO. REPEAT: DO NOT COMPLETELY DRAIN THE BOILER! ONLY ENOUGH TO DROP THE PRESSURE TO ZERO!

4. With an ACCURATE tire pressure gauge, check the air charge in the tank on the air valve opposite the end of the tank that's connected to the system. If ANY water comes out of the air valve, the bladder inside the tank is shot and the tank needs replaced. If no water comes out the air valve, and the pressure is less than 12-15 PSI, continue to step 5. If the pressure is OK, turn the water supply to the boiler back on and repressurize the system, turn the power back on to the boiler, no service is necessary.

5. Using a bicycle pump, or a small air compressor, add air to the tank until you have 12 PSI air charge.

6. Check the boiler pressure gauge again, and if it has risen off ZERO, drain some more water from the boiler drain until it is again at ZERO.

7. Check the air charge on the tank again. If it is below 12 PSI, add air to the tank until it is at 12 PSI.

8. Repeat steps 6 and 7 until the boiler stays at ZERO and the tank stays at 12 PSI. At this point, the tank is properly recharged and the water supply can be turned on to re-pressurize the system, turn the power on to boiler and return to service.

----------------------------------------------------------------------------
 
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Old 12-29-14, 10:58 AM
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Thanks for the quick response. I did plan on shutting the boiler off, and repeating the process to ensure the correct pressure in the tank.

Does the fact that it didn't over pressurize the first time it cycled, but did the second signify anything?

The bleeders are the automatic type.
 
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Old 12-29-14, 11:09 AM
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Does the fact that it didn't over pressurize the first time it cycled, but did the second signify anything?
Only that ALL the water in the system wasn't hot. The hotter the water of course the more it expands. If the boiler was hot, but the baseboards were not AS hot, the second time it fired, more of the water got hotter and the pressure went a bit higher.

This sometimes confuses the issue with multiple zoned systems as well... if ONE zone calls for heat and gets hot, the tank might have just enough air to handle that amount of expansion... but when more than one zone calls and more of the water gets hot, the expansion capacity is not there to handle all of it.
 
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Old 12-29-14, 11:30 AM
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That makes sense. We'll see how it goes tonight!!!

When I drain the boiler, I could also drain off one of the drains at the zone valve couldn't I. Just thinking it might be easier to get a bucket or something under than the boiler drain which is close to the ground.
 
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Old 12-29-14, 11:40 AM
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You can use any drain on the system. Whichever one is easier, or whichever valve is in better condition... because old valves that haven't been opened in decades are not very likely to close and not drip after closing again.
 
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Old 12-29-14, 02:19 PM
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Just turned off boiler, gauge reading 21 psi. Checked tank pressure prior to starting, 9psi.
 
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Old 12-29-14, 02:58 PM
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gauge reading 21 psi. Checked tank pressure prior to starting, 9psi
That 9 PSI on the tank was with the 21 PSI still on the boiler?

If so, something is wrong, either your boiler gauge or your tire gauge, or both.
 
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Old 12-29-14, 03:33 PM
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Correct. I should have measured it a few times with the gauge before starting but I didn't. That first reading is for sure off looking back because A. The tank was full of water, and B. When pressing the valve, you couldn't even hear any air escaping. Did a few iterations of the flush. Tank was for sure full of water. Bladder seems in tact, no water leaking out schrader valve. Set tank to 12 psi, boiler at 0, opened all the valves, fired it, and so far so good. Is the little air valve above the expansion tank supposed to be tightly closed or loose? Only had one auto air valve to close right by the pressure gauge and T&P valve.

Will check it periodically over the next few days to see if everything holds up.
 
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Old 12-29-14, 04:12 PM
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Is the little air valve above the expansion tank supposed to be tightly closed or loose?
If it looks like this:


image courtesy amazon.com

then yes, that cap should be loose for normal operation.

If it leaks water, close it again, open it every couple days to vent any air that might be in it for the next couple weeks or so, and plan on replacing it over the summer.
 
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Old 12-29-14, 04:37 PM
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Ok thanks. The one by the gauge was loose,but the one above the tank was tight. I will loosen it and see.
 
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Old 12-30-14, 04:51 AM
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I tried loosening the cap by hand, but it wouldn't budge. Should I try with a pair of pliers?

All in all, I drained about 5 gallons of water out of the system.
 
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Old 12-30-14, 07:51 AM
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Should I try with a pair of pliers?
No, I wouldn't.

You could end up with a leak and then yer 5cr3w3d.

Leave it alone till spring/summer when you can replace it.
 
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Old 12-30-14, 08:05 AM
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That's what I was thinking.
 
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Old 01-05-15, 07:57 PM
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Expansion tank still working perfectly!! Thanks NJ, you are the man!!
 
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