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water boiler heater high pressure worries


sammus's Avatar
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02-12-18, 10:15 PM   #1 (permalink)  
water boiler heater high pressure worries

Hi all.
I have an ACK-O-MATIC gas boiler at my 1800 square feet tri level house,that worked beautifully for the last 10 years(only had to change the pump once 6 years ago).but recently,it stopped heating the house,i noticed the psi in the pipes went down to almost 0. I changed the water pressure regulator,flushed the system(3 zones), it worked but psi fluctuating,40 at times.I then changed the expansion tank,flushed the system,it got stable. at these numbers: 14 psi when boiler is not working, and 26,sometimes 28 psi max when water in being heated. producing enough heat, for the house.I am anxious about the pressure.it never went over 30 though after the last changes.but are these numbers reasonable?
Thank a bunch for any helpful advice.

 
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PJmax's Avatar
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02-12-18, 10:33 PM   #2 (permalink)  
Welcome to the forums.

14psi at idle is pretty normal. I'd say 26psi is at the top edge of where your system should be. That high pressure is caused by your pressure tank. It's possibly not big enough or there is not enough air in it.

You want to avoid having to drain and flush the system as that adds new minerals and air back into the system.


~ Pete ~

 
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02-17-18, 11:39 AM   #3 (permalink)  
Thank you for the reply.
I installed a 4 gallon expansion tank. still the same.shall i add air to it? it's brand new,set for 12psi.do you think i should install an air separator/eliminator? someone told me about them.
Thanks.

 
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02-17-18, 12:15 PM   #4 (permalink)  
I'm not a boiler pro. I can't offer a comment on the size of the expansion tank.

I don't think your issue is air in the system. Air is compressible and water is not. When the system heats up the water expands. The pressure tank is supposed to allow that expansion to occur inside of it. It almost sounds like the system isn't seeing the pressure tank. Is there a valve to it that could be closed ?

A few pictures of your setup there could help here... How-to-insert-pictures


~ Pete ~

 
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02-17-18, 04:25 PM   #5 (permalink)  
S,
The 14 is fine if it is enough to reach all 3 floors. Personally, I prefer 18-20 PSI but with your expansion situation it doesn't look like that is possible.

If the tank is sized properly for the system there typically should be no more than a couple of lbs. difference between the cold and hot temps.

I would look at an under sized tank or a bladder with low air pressure.

If you replaced the tank with the same size that had been working problem free for 10 years, I would check the air charge in the tank and charge to at least 14 PSI since that is what your cold pressure is.

When your boiler is up to temp, with a screw driver tap your tank. The top should sound solid and the bottom hollow because of the bladder.

If both top and bottom sound the same, (solid) then your bladder has either ruptured or lost its air charge. In either case it must be recharged or replaced.

Hope this helps a little.

 
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02-17-18, 04:39 PM   #6 (permalink)  
He just installed a new tank... charged to 12psi. That's what's puzzling.
Will upping the charge to 14psi make that much difference ?


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02-17-18, 04:47 PM   #7 (permalink)  
PJ,
No it won't. From 12-14 is minor. Why I mentioned 14 is because in a perfect world you want your tank charge to be the same as your cold water pressure in the system.

12 should be fine if in fact he has 12. That's why I mentioned checking his tank to see if something happened to the bladder.

That expansion tank or lack there of would be the only cause of excessive pressure between cold and hot temps in the boiler.

Proper expansion room would alleviate the problem.

 
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02-18-18, 03:27 PM   #8 (permalink)  
Thanks again for your help.
I tapped the tank while water is hot,top is hollow the bottom is solid( it sits upside down).
I don't see a problem there.i took photos to show you.the pipe between the air vent valve and the water pressure regulator is clean i checked it no blockage,by the way the air vent spits nothing but water when i release it(that's why you see rust on the boiler's top surface.

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02-18-18, 04:12 PM   #9 (permalink)  
S,
So we know you at least have air in the bladder although that tapping test will not let you know how much of a charge.

If you are still getting that much of a swing something isn't right because at those figures you couldn't raise your cold pressure if you wanted without hitting the 30 PSI safety limit.

Do you have any cast iron rads or cast baseboard in your system or is it all just regular copper finned tube baseboard.

Any cast iron emitters requires a larger tank.

Just a thought.

 
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02-18-18, 08:22 PM   #10 (permalink)  
copper finned tube baseboard with tons of fins all around the house.
man. i'm thinking of flushing the whole system again zone by zone.i must have caused air bubbles when i changed the parts. as at first i bought a 2 gallon expansion tank,pressure was still going over 30..
While it never exceeded 28 psi since i got the 4 gallon tank(but after the last installation i did not flush nothing).

 
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02-18-18, 08:35 PM   #11 (permalink)  
By flushing are you talking about bleeding the system.

If you drained the system to put the new tank in and didn't bleed it you're probably loaded with air. It wouldn't hurt to bleed your whole system again.

 
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02-19-18, 01:51 PM   #12 (permalink)  
The new expansion tank has an acceptable volume of only 2.5 gallons of water and is too small for a system with standing cast iron radiators. A better choice would have been the HFT90 with 11.5 gallons of acceptance. The one you have may work but just barely.

 
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