Grundfos pump bypassing?

AlHuurman

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

hot_rod

Send a pic. You don’t usually get gravity flow through a thermostatic mix valve, they have a lot of flow restriction inside them

Jamie Hall

The Grundfoss -- like any centrifugal -- has a remarkably low resistance to flow just going through it. Little more than an open globe valve.

Big Ed_4

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 ?

Larry Weingarten

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

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

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😳