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Grundfos pump bypassing?

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AlHuurman
AlHuurman Member Posts: 2
in Radiant Heating
1My radiant floor is staying warm. Set up is 3 way mixing valve with Grundfos recirc pump.
The pump is off, but the floor is warm.
The system is 10 yrs old, and used to work fine.
Question...is there an internal bypass in the pump, or perhaps the check valve is stuck open? allowing flow to circulate even when the pump is not operating.
Best guesses and resolution? thx folks

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  • hot_rod
    hot_rod Member Posts: 22,189
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    Send a pic. You don’t usually get gravity flow through a thermostatic mix valve, they have a lot of flow restriction inside them
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Jamie Hall
    Jamie Hall Member Posts: 23,360
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    The Grundfoss -- like any centrifugal -- has a remarkably low resistance to flow just going through it. Little more than an open globe valve.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Big Ed_4
    Big Ed_4 Member Posts: 2,788
    edited January 9
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    You may get a flow through the system but since it is a radiant system the tricke through could not hurt ....What is the issue ?

    There was an error rendering this rich post.

  • Larry Weingarten
    Larry Weingarten Member Posts: 3,309
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    Hi, Pictures would help. If there is flow through the pump when it's off, you could install a spring check valve downstream of it. These valves are available with different opening pressures, but probably one with a 1/2 pound "cracking pressure" would prevent "ghost flow". If the system is tall, as in multiple stories, you may want a valve with a higher cracking pressure.
    Yours, Larry
  • AlHuurman
    AlHuurman Member Posts: 2
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    OK thx guys...

    Big Ed - the issue is that I don't have control of the heat...it's heating the room all the time. It's not too warm but is only used on weekends

    Larry - Don't most of these Grundfos come with a built in spring check valve?

    Pic attached.

    The arrangement is I think pretty typical of radiant heat loop off the main loop...the mix valve controls the floor temp to approx 100F. The circ pump turns on/off with the thermostat. The remainder of the house is fin radiators. The location of the room is on the other side of this concrete wall, and the floor is approx 8' lower than the penetration through the wall. Note that the system worked well for 8 years, but the last couple of years seems to be leaking past the circ pump. Wondering if I should replace the pump with a zone valve? or maybe just remove the pump to see if the check valve is stuck open?
    Hard to see from the pic, there are 2 loops in the room of approx 400 sq ft
  • hot_rod
    hot_rod Member Posts: 22,189
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    Some of early pumps you had to insert the check, it was loose in the box. Maybe you don’t have a check. But if it worked in the past, it could be a stuck or bad check.

    If it has a big check mark on the label, it is a check pump, IFC.

    The pump is mounted outside, and not wired exactly to code😳
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream

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