Replacing expansion tank on boiler

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  #1  
Old 11-10-18, 08:52 AM
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Replacing expansion tank on boiler

Hello, this week I noticed water filling the bucket under the boiler TP relief valve. I checked the schrader valve on the expansion tank and confirmed that the bladder has failed and it is filled with water. I purchased a replacement tank (Amtrol 30 EXTROL pre-charged to 12 PSIG. 4.4 Gallon Volume).

Iíve mapped out my system, read a lot about the job and feel ready to tackle it.

This is the procedure I plan on:
  1. teflon tape threads of new tank (leave top 2 or 3 threads bare)
  2. fill tank to 15lbs to match boiler (2 story home, boiler in basement)
  3. turn off boiler, allow to cool to 100 degrees F
  4. turn off all 4 valves on boiler system
  5. drain boiler to 0 psi from drain on bottom right using washing machine hose & 5 gal bucket
  6. close drain
  7. unscrew old tank using wrench on the top fitting (I understand it will be very very heavy and may try to drain it first)
  8. screw new tank into place
  9. open water feed valve slowly and pressurize boiler to 15#
  10. open the remaining 3 valves, turn on boiler power & set the thermostat to call for heat
I have a few questions before I replace the expansion tank on my boiler.
  1. Is it necessary to shut off all boiler system valves or just the water supply valve? If it is all, is there a specific order to shutting them off?
  2. The water supply valve is the one on the left, above the back flow preventer?
  3. Will I get air in the system with this replacement? If yes, how to purge it?
Thank you for any advice or comments.
 
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  #2  
Old 11-10-18, 12:22 PM
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Pete,

After shutting off power to the system you can:

1) Close your ball valves on your SUPPLY, RETURN, & BOILER FEED.
2) Next, instead of draining the whole boiler, open up your relief valve and remove pressure from there. Your relief valve is below your line to your tank so that will remove any water above the point of the tank and save you from removing more water than needed.

If the tank is full it will weigh about 35lbs., so if you want you can drill some holes into it and drain in a bucket or take it off as is.

A suggestion would be that while the tank is off to add a ball valve and a spigot on that line to make future replacement or maintenance easier in the future.

Reinstall new tank and fittings if so inclined and open ball valve on FEED to pressurize boiler.

You have a Spirovent on there which should remove the little air from the fresh feed if you drain from the relief valve.

If drained as suggested you will lose so little water and with your spirovent to remove air you may not even have to bleed anything.

After boiler is pressurized and you hear no more air, open your ball valves on the SUPPLY & RETURN lines and turn on boiler to test. You should be good to go.

Hope this helps a little.
 
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Old 11-10-18, 02:36 PM
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Your system drawing shows a "T/P" relief valve. T&P reliefs are usually used only on hot-water heaters. Your heating boiler should have a regular relief valve set at 30 psi.
 
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Old 11-11-18, 06:49 AM
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That helps a lot spott,

I think I will drill out holes in the tank, I don't want to try to remove / catch it at the same time. It will be just me on this job.

Using the relief valve will be a more convenient alternative to using the boiler drain. Do I still drain it to 0 psi? Or drain until it stops flowing?

I would like to add a ball valve and spigot on the expansion tank line. I found a thread with a good picture...that's what I want to do. I just need to identify the correct parts.
Thanks again
Pete
 
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Last edited by peter68; 11-11-18 at 07:11 AM.
  #5  
Old 11-11-18, 06:52 AM
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Thank you gilmorrie, I looked at the tag and that is exactly what it is - a regular relief valve set at 30 psi. I will correct my drawing.
 
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Old 11-11-18, 07:28 AM
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I would like to add a ball valve and spigot on the expansion tank line. I found a thread with a good picture...that's what I want to do. I just need to identify the correct parts.
You can use standard parts or one of these:

https://www.supplyhouse.com/Webstone...iABEgKa7PD_BwE
 
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Old 11-11-18, 08:08 AM
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that looks a lot cleaner, thanks 2john2458.

I was looking at this one:
3/4" Pro-Pal Full Port Forged Brass Ball Valve w/ Hi-Flow Hose Drain & Reversible Handle

I thought the line was 3/4" and I needed 3/4" parts, is that wrong? Your part suggestion is 1/2". Also your part has an extra outlet, is that needed? Thank you very much for your answer.
Pete
 
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Old 11-11-18, 10:20 AM
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That expansion tank is only 1/2" and that's all you need and they are just regular fittings and you can install them whatever way is most convenient for you. You can remove that 1/2" nipple and get some shorter ones and include your valve and spigot.

You only need to drain until it stops from the relief valve which I believe will be probably 0 PSI on the boiler even though you still have water in there with the open system it still may read 0 so don't worry.

Because of the location of your tank if you don't want to drill holes to empty you can get a big bucket or container and just let it drop into it.
 
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Old 11-11-18, 12:57 PM
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i think i have got it now, thank you. i'll put together an assembly tomorrow morning, and hopefully post some pics by the afternoon.
 
  #10  
Old 11-12-18, 10:25 AM
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Alright, I believe I've done it. Here are some pics of the job. It felt insurmountable a couple of days ago but you guys made it doable...thanks. Some notes:
  • Yes, that tank was really heavy, luckily mine is mounted low so I put a plastic bin topped with a heavy board just below it. Once it fell i just needed to catch the balance...the only challenge was several cups of hot water running down my hands. The old tank was full to the brim and took a while to empty into utility sink.
  • Making the new nipple/valve/spigot assembly was easy. I just needed to try to match the length of old assembly in order to clear the pressure relief valve assembly. The hard part here was making the two valves line up...I would crank one tight and the other would twist around back, so that took a bit of fiddling.
  • After re-opening the feed valve my spirovent tick ticked away with small bubbles, so I let it sit for 90 minutes until it was completely silent. Once I opened the supply and return valves a significant hiss of air went through it. I have no clangs or bangs in the radiators so I think all is ok there.
Thank you Spott and the rest who replied. You showed me how to do it, it's a great feeling to do a job yourself but also to get a better understanding of your heating system.
 
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Old 11-12-18, 10:54 AM
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Peter,
Thank you for the update. The trick to putting pipe and fittings together is to use 2 wrenches. One for tightening and one on the stationary piece so it doesn't move.

If you needed a little more room for your spigot you could have added a short nipple and a coupling from the tee and then add your tank but it looks good.
 
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