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Rick, HVAC Supervisor
Category: HVAC
Satisfied Customers: 21386
Experience:  40+ yrs. experience as a licensed oil & gas technician.
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Is it possible that a fifty year old, Taco flochek fifty

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JA: Hi. What is your issue regarding?
Customer: Is it possible that a fifty year old
JA: I'll do all I can to help. How long have you been dealing with this?
Customer: Taco flochek fifty years old jammed and causing overpressurising in the boiler. Possible?
JA: Do you plan on doing the work yourself?
Customer: I am
JA: Anything else we should know to help you best?
Customer: I've gone through everything from changing the aquastat to replacing the feed regulator valve.

Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. If my initial response doesn’t answer your question then let me know and we can continue our conversation.

Flow checks don't cause over pressure problems. Since you've replaced the feed valve the only other likely culprit is a failed expansion tank. Or if it's a 50 year old expansion tank hung up between the floor joists it water logged and needs to be drained.

Customer: replied 9 months ago.
Hi Rick,My name is Stan, this experience of writing questions like this is new to me.I've changed the expansion tank as well as the feed flow regulator.I replaced the aquastat last year and the cut in and cut out are performing just as set.I've recently replaced the circulator pump (one zone).The furnace is an American Standard that was installed in 1972.When the overpressurizing first occurred I thought possibly the tankless coil might have a leak but I've tested by elimination this possibility.The temp/pressure gauge always returns to 12 PSI when the boiler cools but by the time the temperature on the gauge reaches 170 (following the aquastat setting exactly) the pressure bumps just up to 30 31- 32 PSI. The PR valve (also new) vents the pressure.The only other peripheral valve or gadget that hasn't been changed is the taco 220 flo check. It has a thumb screw on top (which the taco folks say can be opened to allow for heat to circulate should the circulator fail)One oldtimer on a blog thread said that he had seen old ones that had failed and negatively impacted flow and lead to overpressurizing.I appreciate the time you take to respond to this question. I intend to change it this weekend in any event.Any further input you provide will be considered.Thanks very much.Stan

Since the pressure " always returns to 12 PSI when the boiler cools" this indicates this is an expansion problem. If you have a new expansion tank it may be too small. I need to know the btu input of your boiler and the type of radiation (copper baseboard, cast iron baseboard, cast iron radiators, convectors) you have. Like I said before a failed flow check can't have any impact on system pressure; flow yes, pressure no. I wouldn't go through the trouble of replacing the flow check in this case if your intention is to fix a pressure problem.

Customer: replied 9 months ago.
the replacement expansion tank is the exact same unit as has been on the unit for as long as I can remember.
The expansion tank is hung from the flow check. It's bushed down from 1 inch to one half inch. In between the reducer bushing and the tank are fitted one 90 degree angle , a four inch nipple, another 90 degree angle, and then the expansion tank.
The fittings just mentioned are black iron.
Is it possible that the years of use have led to a build up of crud or some such matter at the two nineties that the expansion tank isn't accommodating the pressure rise in the boiler?
Again, the other variables you mentioned don't seem to be the issue as the entire hydronic configuration as worked reasonably well as is since 1972.

A clogged fitting is possible. That said you can't rule out the expansion tank until you answer my questions related to sizing. It doesn't matter if that size tank worked before.

Customer: replied 9 months ago.
Hi Rick,Just got down to the cellar and found that the expansion tank I used to replace the original is charged to 50 psi.
It's an Amtrol Therm-x-troll model st 12 used for potable water.The original is an extrol model #30 charged to 12 psi.Shame on me for not verifying the correct order when Amazon delivered it.They're both 4.4 gallon capacity. Would it be acceptable to simply back the air pressure off on this one 50 - 38 = 12?12 PSI is what the extrol model 30 (original) is rated.Whaddya think?Thanks
They're both 4.4 gallon capacity.

Ok, that's a water heater expansion tank it's not for a heating system. An Extrol 30 is the right one for heating systems and is the common size for an average system. I've never used a water heater expansion tank on a heating system but the principle is the same. You could try dropping the charge to 12 psi but you must do that with no pressure on the system.

Customer: replied 9 months ago.
When I've drained down the boiler can I simply bleed off the air pressure from the tank?Or should I drain the system down, remove the expansion tank, adjust it to the required PSI, and then reinstall and refill the system?

Yes, you can leave the tank in place and bleed off the excessive pressure. You don't have to completely drain the system just drop the pressure to 0.

Customer: replied 9 months ago.
I'll give it a go shortly and report back to you later on today or tomorrow.Thanks for asking the right questions.

You're welcome. I'd appreciate a favorable rating

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