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Old 11-05-2011, 11:25 AM   #1
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hydronic system pressure question - normal?


I recently replaced/upgraded the (bladder-type) expansion tank on my 2-zone hydronic heating system. The expansion tank would inevitably fail like clockwork about every 2 years - waterlogged, popped bladder or whatever. It turns out the #15 tanks I had been using were too small for my 90MBH boiler, so I replaced it with a #30. While I was at it, I also replaced the air scoop & relief valve.

I purged and re-filled the system, and checked/adjusted the fill valve so that the gauge read 12psi with the boiler cold.

Now when the burner runs, the pressure increases to a maximum of about 20-21 psi when the boiler reaches its 180 set point.

Is this nornal? I seem to remember that previously it would only increase by a few psi (to maybe 15-18) during a burn cycle.

Any advice or info is much appreciated.

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Last edited by johnnyzero; 11-05-2011 at 11:29 AM.
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Old 11-05-2011, 11:37 AM   #2
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hydronic system pressure question - normal?


Baseboard or radiators?

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Old 11-05-2011, 11:41 AM   #3
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hydronic system pressure question - normal?


I'd be satisfyed with 20 psi on your boiler running at 180 F.
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Old 11-05-2011, 11:42 AM   #4
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hydronic system pressure question - normal?


finned baseboards.
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Old 11-05-2011, 12:07 PM   #5
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hydronic system pressure question - normal?


So you think 20-21 psi is a-ok and normal. Good - that's what I wanted to hear.

thanks,
JohnB
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Old 11-05-2011, 12:15 PM   #6
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hydronic system pressure question - normal?


btw, the other problem I had with the smaller #15 tanks occured whenever I fired up the boiler from a cold condition (if I lost power for an extended period of time or went away on vacation). As the boiler water came back up to temperature, the pressure would climb way too high and I would have to bleed it off several times to avoid tripping the blow-off valve.

With the bigger expansion tank, this issue seems to be resolved.
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Old 11-05-2011, 12:30 PM   #7
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hydronic system pressure question - normal?


that's fairly normal 10PSI below dripping on the relief not that that is so accurate place a plastic bucket under it so to see if water drips...your good...i have a metal tank mounted above a one level cape cod pipe comes off the supply out of a weil mclean hot water baseboard system has a drain cock on it no bladder and drainable(isolating valve. simple expansion might consider that...180F water on bladders under pressure....take the wife to dinner instead...normal PSI..cold boiler sits at the RED regulator feed typical 12PSI then heats to 180F as yours 20psi stat satisfies...might want to lower that limit to 160F see if you satisfy the house control is very liberal TO SEE ACTUAL SETPOINT when the main gas shuts off but the circ pump stays ON that is your control setting no matter what the dial says...cheat a little hand out some swets and long johns keep in mind what water temp to you need to make 70F setting. wind blowing below 30F boiler will run longer during to wind chill treat the troops to a reset up.if you turn the limit scontrol just after it goes off with the circ on you'll se the main burner wil light that is the temp check the thermometer.... on the boiler.

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