hot water radiators always hot

One of the zones in my house is always hot. Even when the circulator pumps are off (The pumps will turn on fine if you crank the thermostat up.) I have a hot water boiler system with baseboard radiators. There are two taco circulator pumps(007-5F, No IFC) on the return side, and two taco flow check valves(221-1) on the supply. The only thing I can think of that would cause this is that the flow check valve is leaking or stuck open. Is there anything else that would cause this? If it is the flow check can one replace just the stem or does the whole assembly have to be replaced?

 

No actual experience with these Flo check valves, although I do have them on my heating system.
Just reading up on them I find they can get stuck and sometimes just a tap with a hammer may help them to close again. But it may just be temporary fix, since the reason may be that it got crudded(?) up.
They apparently do have replacement stem and parts but of course you have to be able to isolate it from the system in order to avoid having to drain the system down. May want to wait til warmer weather returns if that's the case.
If you can isolate, you could try just removing the stem components, clean things up and put back together. That may be enough.

 

What kind of zone valves do you have??

 

@TomFOhio There are no zone valves. Two circulator pumps and two flow check valves one pair for each zone.

 

So I tried out the "tap with a hammer" strategy. The zone seems to be controlling properly. This confirms my suspicion of the flow check valve being the problem. Thank you so much! Let's see how long this lasts.

 

Could you take a snap shot of your check valve in question.

 

Glad to hear it!
During the warm weather, and when your feeling ambitious, you can consider opening it up and cleaning it out a bit.

 

Here is the supply side, the return side, and the flow check valve.