Diagnosing faulty boiler expansion tank

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Old 01-19-20, 06:36 AM
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Question Diagnosing faulty boiler expansion tank

Good day all!

Last November, I had issues, which were resolved; There was a question of a water leak fireside, which was not the case.

On to a new problem, and yet remarkably similar.

My boiler has once again started to lose pressure; And once again, I traced every inch of pipework throughout the house, and found no leaks; On the assumption that nothing has changed inside the boiler in the last two months, I'm going to assume it's not a fireside leak, so that left the expansion vessel.

I removed the shrader valve cover, pressed it in, and water came out; Not at any pressure, but water nonetheless. The expansion tank needs replacing, that much is true; The current tank is a Bell & Gossett 1BN203 (HFT-60). I intend to replace it with an Amtrol #60. Can anyone confirm if this is a good replacement? Unfortunately I can't find any local stores that keep a 7.6 gallon expansion tank in stock, so it'll take a few days, so I thought, being Sunday, I'd ask my favorite DIY forum if this is a good replacement.

Another question I'd like to ask is, how is the system drawing in air? It makes sense that it is, because as the water expands, it's leaking out of the pressure relief valve, so when it cools it wants to fill the void, but how is it doing that? (what component is allowing it?)

Is there anything I can do to patch the system between today and when the tank arrives? (I don't want to flush the system daily with fresh water, as I read it can do damage)

Also, I just discovered that the watts air vent needs to be replaced, so that will happen at the same time.

Thanks in advance for any responses. As always, they are much appreciated!
 
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Old 01-19-20, 09:52 AM
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I'm not the boiler pro.

The pressure tank acts like a cushion to keep system pressure balanced and have a place for the water to go when it expands. When that tank goes bad and fills up with water...... there is no cushion and the system pressure rises.... not falls... as the water heats up. Your water fill valve should keep the system charged to at least 12psi by design. Many fill valves have a manual position or arm so that you can add water manually.
 
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Old 01-20-20, 09:15 AM
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[/QUOTE]BritinMa: Unfortunately I can't find any local stores that keep a 7.6 gallon expansion tank in stock, so it'll take a few [QUOTE]

Gave up on local stores because they are often twice price of HomeDepot.

Supplyhouse.com is often half HomeDepot price with next day delivery. Extrol 60 is $65: https://www.supplyhouse.com/Amtrol-103-1-60-Extrol-Expansion-Tank-76-Gallon-Volume-2558000-p

Amazon is $97
https://www.amazon.com/Extrol-Expans...9534531&sr=8-2
 
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Old 01-20-20, 10:27 AM
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As far as your current #60 extrol being the right one without knowing what you have for a system it's difficult to say. I can tell you sight unseen that if you have any cast iron rads or baseboard that you are heat that is the minimum size you need.

If you are getting water out of your Schrader valve that is an indication that your bladder has given out allowing water to fill your entire tank without the needed cushion needed for water expansion when it is heated. It works on the same principle as an overflow tank in a car. As the water in the rad gets heated it goes into your plastic overflow.

As for how air gets into your system, as PJ mentioned you have an automatic feed valve that when working properly and when the manual valve is left open in front of it keeps the boiler at a fixed pressure. As water is released from the relief valve and drops below that setpoint the feed valve automatically opens and lets fresh water into the boiler which brings air with it which is the boilers worst enemy.

The sizing chart below may give you some insight as to what you may need.

https://www.amtrol.com/wp-content/up...nSight-Cap.pdf

https://www.supplyhouse.com/sh/contr...SizeCalculator

Hope this helps a little.
 

Last edited by spott; 01-20-20 at 10:44 AM.
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Old 01-20-20, 03:56 PM
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Expansion tanks size is based on volume water, temperature range and other factors. The sizing charts in #3 Post links to Amtrol and Supplyhouse calculators do not use water volume. Sizing from both is not reliable.

Amtrol and Supplyhouse require boiler BTU capacity, not volume. Both give wrong size #30 for my 150,000 BTU system. Mine requires #60 to maintain stable system pressure.

In link below Volume is first item in formula on third page page (62).

http://www.taylor-engineering.com/We...sion_Tanks.pdf
 
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Old 01-20-20, 04:05 PM
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Thank you all. I used the Amtrol site yesterday; My piping is copper, and my baseboards are copper/fin.

The faulty tank is a 7.6, and this is a direct replacement for it, I believe.

I ordered it today, and it should be here before the weekend..... Will report back!
 
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Old 01-20-20, 04:21 PM
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Amtrol and Supplyhouse require boiler BTU capacity, not volume. Both give wrong size #30 for my 150,000 BTU system. Mine requires #60 to maintain stable system pressure.
It also said I should get a 30 (it was right on the 30/60 limit), but the 60 was a direct replacement for the Bell & Gossett (7.4 gallon volume, 2.5 acceptance) and the dimensions are identical.
 
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Old 01-20-20, 06:25 PM
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The basic point in my #3 Post was expansion tank sizing based solely on boiler BTU is not reliable for all systems.

Old systems often have much higher volume than new ones so adequate size data is important. And... usually there are no issues with over-sized tank.


 
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Old 01-20-20, 07:02 PM
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BritlnMA, Be prepared for some serious weight when you take that old tank off. If the tank is full, be prepared to handle 70+ pounds.
 
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Old 01-21-20, 02:26 PM
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BritlnMA, Be prepared for some serious weight when you take that old tank off. If the tank is full, be prepared to handle 70+ pounds.
Thanks; I was considering using a cargo net underneath it; Not entirely sure it would hold 70lbs falling onto it, so will have to either ensure it's real close, or come up with another idea.

Thanks!
 
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Old 01-21-20, 09:08 PM
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That's exactly why I'd drill the tank. Once the water drains, the empty tank is easy to handle. Have a couple of buckets handy.
 
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Old 01-22-20, 07:31 AM
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That's exactly why I'd drill the tank.
I've no issue doing that - do you have a preferred method? Drilling out the valve, or a "new" hole in the base of the tank?

Also, I believe I must replace the pressure relief valve; The current one is an Apollo 10-400; since this all began, I've been checking on the boiler 2-4 times a day, emptying the bucket beneath the pressure releif valve (not even a quarter gallon per day was being dumped), as well as testing the pressure relief valve. Today, the valve gave more resistance than usual; I checked the system pressure and it was higher than usual by about 7 psi; A firmer grip on the valve released it; it's working perfectly fine now, but I am now concerned about a high pressure build up.

Needless to say the boiler is off, and I'm off to a big blue box DIY store and will be replacing that valve today. Unless of course, by the time I return, someone tells me I'm over reacting!

Thanks for all the input so far - very much appreciated!
 
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Old 01-22-20, 11:27 AM
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I suspect the relief valve issue is due to the bad tank. Personally, I'd replace the relief valve & the tank at the same time. That way you only have to drop the system pressure once. As to drilling the tank: I drill a hole near the air valve & another near the top of the tank. You should be able to just remove the valve core using a tool for the purpose available at any auto parts store. Alllow as much water to drain as will before drilling.
 
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Old 01-22-20, 12:41 PM
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Thanks Grady!

I will be replacing three key components then; The pressure relief valve (out of stock a the local blue box!), the expansion tank and the watts air vent.

I'll report back when it's all taken care of - hopefully tomorrow or Friday.
 
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Old 01-22-20, 02:57 PM
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Any plumbing supply house should have relief valves in stock.
 
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Old 01-22-20, 02:57 PM
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BritInMa might want to consider putting shut off valve on expansion tank. For future system jobs will make depressurizing system easier. Then after shutting off valve, can just drain a little water to depressurize.


 
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Old 01-22-20, 02:59 PM
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Good suggestion. Yes it does make future work a lot easier as long as there's room to install it.
 
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Old 01-22-20, 03:11 PM
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Also consider putting unions on either side of pressure/relief valve. They often have to be serviced which is easier when removed.
 
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Old 01-22-20, 03:46 PM
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Valves on both sides & at least one union between a valve & the reducing valve. Never had a need to have one on the relief valve.
 
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Old 01-22-20, 08:37 PM
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Many systems have Combination (Dual Unit) Valves that combine the functions of pressure reducing (fill) valve and a non-code pressure reducing relief valve. Removing the complete assembly is the most practical way to service either of them. https://www.supplyhouse.com/Bell-Gos...alve-Lead-Free
 
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Old 01-23-20, 02:07 PM
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Everything is done, and it's all working again. I took a few pictures, but honestly there's really nothing much to see.

Given the current weather up here, I didn't take the extra time to put various valves in; we are extending the heating system later this summer, and will take the opportunity to do all of that at the same time.

Work done today: Replaced high vent (watts air vent), replaced expansion tank, replaced pressure relief valve. Total time taken: under 2 hours.

Before filling, expansion tank read approx 13 PSI
After filling, I let it go high; pressure relief valve opened at approximately 32 PSI.
I heard the high vent venting, but then did a rapid vent (I have one valve at the highest point).
After purging air, I reduced the pressure to approx 13 PSI at cold; expansion tank read approx 15 psi.
Fired up the boiler, and tested. Once up to heat, top 1/3 of expansion tank was warm, bottom 2/3 cold.

So far, it's working well, but I'll be keeping a close eye on it for the next few days.

Thanks again to everyone for your responses.
 
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Old 01-23-20, 05:49 PM
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Glad things went well. Thanks for the follow up. So often we never hear from folks once the problem is fixed.
 
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Old 01-24-20, 03:03 PM
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I am a fan of following through lol

Over a day in, and the heat in the house seems more even. Not sure if that's real or perception.

Again, many thanks for the input, everyone!
 
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