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ALNY Member Posts: 37
edited January 2015 in Radiant Heating
I have my boiler, and i had to replace the inlet because of complete rust blockage.
I replaced it with a Taco 334-T3, all was working fine, and pressure was at 15-20lb.

2 months later i get a call from my tenant, and the Grundfos pumps were banging, and making tons of noise.
They were shot. I replaced them, and all was fine, when i noticed that the pumps were whining, and i saw the temp gauge at 220 and PRV was leaking. I imediately cut the boiler, and waited till temps dropped....i saw that Aquastat was shot due to the fact that the Taco 334-T3 was dripping all over it. So i replaced aquastat as it was faulty, and now it works.

The boiler falls to 15 PSI when off, but second it calls for heat, pressure builds up to 30lbs, and PRV leaks....i lowered temp on the aquastat to 160, and its manageable for now.....I m thinking of replacing the expansion tank as most likely the culprit ....any thoughts??? I am also thinking that city pressure may be too high, but wouldnt 334-T3 fix that?


  • That rust blockage that you fixed could have been the result of continuous make-up water malfeasance. Check the expansion tank; replace if necessary and check all the piping that connects the expansion tank and fill valve to the boiler. If it is clogged, it can isolate the expansion tank from the system which will bring about symptoms that you are experiencing.

    Your Taco 334-T3 should take care of reducing city water pressure to 15 psi.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • Ironman
    Ironman Member Posts: 7,350
    The expansion tank is indeed the first thing that comes to mind. If it's a bladder tank, momentarily depress the schrader valve on the air side. If you get water, the tank is shot. If not, the air side should be pressurized to match the setting of the fill valve, 12 psi min. This should be done with NO water pressure on the hydronic side of the tank.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • ALNY
    ALNY Member Posts: 37
    Will replace tank, and see whats up....thanks!
  • Gordy
    Gordy Member Posts: 9,546
    edited January 2015
    In addition to others. How old is this system. Is radiant done in pex if so is it non O2 barrier, or hard piped copper/black pipe? Seems like pumps are taking a beating.
  • ALNY
    ALNY Member Posts: 37
    Tank was blown ...replaced, and all was good...forgot to update.
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,506
    edited November 2017
    I'd also check your aquastat-the settings vs. the temperature. You may need to replace that also. You don't want you're boiler running up to 220° and steaming. I'm surprised you didn't destroy the PRV.