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non O2 barrier pex restricted in Radient slab with rust from cast iron pumps

scottscott Member Posts: 3
edited September 2016 in Radiant Heating
pumps have been replaced with stainless and system purged, but one particular loop in the slab is very restricted. ive tried blasting it from both directions with 50psi water, and 90psi air compressor. flow improved a tiny bit, but still too low. how to clear? can i push trhough with fiberglass fish tape?

thanks so much,


  • kcoppkcopp Member Posts: 3,596
    Were the manifolds also replaced?
  • scottscott Member Posts: 3
    Manifolds are brass, and flowing, and i've isolated the subject loop during testing.
  • IronmanIronman Member Posts: 6,140
    Fernox boiler cleaner. Add it. Circulate it in the offending loop.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • kcoppkcopp Member Posts: 3,596
    Sometimes the valves on the manifolds can be very restrictive.
  • scottscott Member Posts: 3
    thank you. i have tried hercules boiler cleaner, but it did not do the job. is fernox much more effective?
    it is not the valves, as i had detached the loop from all other components during this flushing attempt.

    has anyone ever used a fiberglass fish tape to push a blockage? i have a fiberglass tape with a small metal eyelet crimped onto the end. i have considered cutting off the eyelet, and smoothing the end, then try to fish down into the loop. im not sure if the tape could bend back and forth through the loops "switchbacks",,?

    i know it could be kinked, but i believe it is most likely clogged with rust sediment, as the failed pumps were packed with the orange sludge, and i blew much of it from the loop.
  • kcoppkcopp Member Posts: 3,596
    The fact you have any flow is encouraging. I second the Fernox. If you can get the solution in there and leave in is in there circulating for a few days that will dissolve it.
  • hot_rodhot_rod Member Posts: 14,374
    You may have magnetite in the tube, it is usually a blackish looking deposit and it settles out in tubes. It can be very tough to flush or dissolve out, like cement :) Some contractors specialize in cleaning the old sludged systems, a carwash type of pump that provides high pressure and a pulsating flow might work, like a mini sewer jetter, insert it a far as possible and let it run for a day?

    Most of the boiler cleaner are a strong detergent, you may need a more aggressive scale buster type of cleaner to dissolve the build up, if it is metal and minerals.

    Most of the chemical providers have both cleaner and scale removers available, Rhomar is another good source of products and info.

    Or the loop could have a kink? If it is just one loop that is a real possibility.

    And in some cases you need to abandon a completely plugged loop or get by with the limited output it can provide.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me

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