Radiant flow not pushing fast enough

beatbox82 · September 9

THis forum has helped me figure out alot of the problems I've had in my home since purchasing it 15 years ago. So here goes.

This past winter was doing reno in main part of the house including kitchen/lr/dr/den all one level ranch. Decided to run radiant heating 1/2" pex tubing, 5 loops all approximately 200 feet each loop.

Connection to boiler was completed and we had heated floors but not all the way through. I have a fireplace insert so was able to supplement the heating by burning wood until Spring 2025.

Fast forward to today, Winter is coming and I was thinking of upgrading the circulation pump that runs that zone to push more water through the loops.

I post pictures of my setup. Running a manifold off the boiler with 4 zones total. Rest of house is baseboard heating. Hot water is separate oilfield burner.

Current circulators are Taco 007 1/25 HP

1/2 pex is set in 2.5" of mud with tile on top

4 zones total. 1 of the zones going to radiant manifold.

Also have taco mixing value 86⁰ to 175⁰

Wanted to install Taco 009 1/8 HP.

How does that sound or will I blow my system up?

Thank you for your expertise in advance.

mattmia2 · September 10

Though not impossible, I don't think your problem is the circulator.

What happens on a call for heat?

Does the heat call get satisfied?

Does the boiler cycle on high limit?

What is the supply and return water temp?

I'm not sure your circulator is in the right place in relation to the thermostatic mixing valve(in fact i think it isn't but i'm not an expert on that).

DCContrarian · September 10

The circulator needs to be on the output of the mixing valve. Right now, when the hot water supply is above the setpoint of the mixing valve the valve will close and there will be no circulation.

mattmia2 · September 10

there will be a little circulation but it will stop when the mixing valve gets to setpoint, then that tube between the circulator and the mixing valve will cool and it will push that slug through, then it will stop again…

hot_rod · September 10

pump away from the mix port on the valve

the return from the manifold also needs to go back to the boiler

if you have a cast iron boiler you may need return temperature protection also

hot_rod · September 10

This is the case regardless of the pump on supply or return piping at the boiler.

mattmia2 · September 10

i'm guessing that is either modern hydronic heating or pumping away.

beatbox82 · September 10

Thank you. To answer @mattmia2

On call for heat, for the first week of running water temp going into the manifold after mixing valve was reaching 120⁰ setpoint and coming back in the 80⁰ give or take.

Then just stopped pushing through and at that point I confirmed pump was hot to touch almost like a electrical short had occurred. This is what made me think that it was underpowered.

Call at first would get satisfied but after some time no. It's like system got tired of pushing water.

Boiler would reach limit and shut off.

It's hard to test now with outside temp still in low 70s. Im on Long island, NY

I thought maybe mixing valve malfunction or pump just died on me. Pump is fairly new maybe 3 years old.

pecmsg · September 10

run the pump without the heater.

Alan (California Radiant) Forbes · September 10

Yes, with your pump getting very hot, it might be fried. Check the amp draw when it’s running. It should be .71-.76 amps. If it’s different, replace it with it relocated properly.

But don’t use a Taco 009. As you can see by the 009 performance curve, you won’t get any more GPM; you’ll get less if the pumping head is over 8'.

hot_rod · September 10

A very hot pump could indicate an air lock, it is not moving adequate or any water to cool the motor.

mattmia2 · September 10

https://forum.heatinghelp.com/discussion/comment/1864399#Comment_1864399

Since the circulator is pumping in to the hot port of the thermostatic valve, isn't the thermostatic valve going to close that port off and fully open the cold port when the outlet of the valve gets to the setpoint. Won't the valve get to the setpoint very quickly when they boiler is up to temp because it will be pushing water that is hotter than the mixing valve setpoint in to it? There will be essentially no flow in to the cold port because the circulator will pull the water that goes in to the loop back to the boiler through the return when the valve is open on the hot side and once it closes the hot side completely there will be no flow at all. I think the combination of hot boiler water and deadheading the circulator is making it hot. That will eventually damage it but it may still be ok now.

The valve does modulate between hot and cold but if the setpoint is like 120 f and there is 160 degree water being pumped in to it, it will go full to cold.

beatbox82 · September 10

To be continued. Im gonna wait for a 50⁰ day and fire it up. Thank you all for your input.

mattmia2 · September 10

Turn off the gas to the boiler or disconnect one side of t-t to the boiler so it doesn't heat or just let it fire to 100 degrees or so and then stop the boiler but keep the circulator running and see if the heat gets all through the loops.

hot_rod · September 10

https://forum.heatinghelp.com/discussion/comment/1864404#Comment_1864404

I suppose it depends on the design of the valve, not all valves shut off the hot port 100%. ASSE listed scald protection valves can shut off the hot 100%.

You should pipe up a few demos and report back :)

Regardless, this is how most if not all three way thermostatic manufacturers require a 3 way thermostatic to be piped, for hydronic mixing use. Piped this way it will work, piped in any other configuration you may not always get the results you expect.

Screenshot 2025-09-10 at 12.46.35 PM.png

EdTheHeaterMan · September 10

Where is the circulator for the Radiant floor zone located? It should be here (see Photo)

You may not need the circulator on the boiler side of the mixing valve as indicated by @hot_rod

Radiant flow not pushing fast enough

Comments

Categories