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can an incorrect system fill blow an expansion tank?

Just looking for some thoughts on the likely cause of a expansion tank failure. 

I recently had an expansion tank fail in an oil fired hydronic heating system.  the system had been bled in order to install a new radiator and in the process of refilling the system it was determined the tank gave way and the expansion tank bladder busted. 

I believe the system was not correctly refilled (specifically someone may have failed to open the backflow value to allow the boiler to fill first, which then forced the water to forward fill an old gravity fed system which covered three floors before water came down the "cold" side and fed the already "cranked up" boiler with water.)  Would this have just created steam for the relief valve to dump?  or could this have blown the tank somehow?  or is this simply a case of bad luck/timing? 

The expansion tank was 2 or 3 years old but i don't recall the make / model.

Just looking for thoughts and opinions.


  • kcopp
    kcopp Member Posts: 4,393
    not likely...

    now there may have been a defective tank. but filing the system....no.
  • Big Ed_4
    Big Ed_4 Member Posts: 2,700
    IT happens

    What happen , the tank was loosing its charge before the repair ... The air needed for a cushion bleed out of the tank and was caught up in the radiators ... Which would still cushion the expanding water .. After the repair the radiators where bleed to remove all the air , along with the cushion ... It happens
    I have enough experience to know , that I dont know it all
  • Gordan
    Gordan Member Posts: 891
    Cranked up boiler

    The scenario you're talking about would involve both dry-firing the boiler and causing thermal shock. It would also likely create quite a ruckus. I'd think that a lot of other things would give way before the tank diaphragm (which is designed to flex) would.

    I personally can't imagine firing a boiler prior to filling and purging a system. If what you're describing really happened, the expansion tank would be the least of my concerns - expansion tanks are cheap.
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