Constant heat in 1 zone

George_15

I have a gas hot water boiler with 6 zones for heating a 2.5 story building, plus a 7th one for hot water with a coil inside the boiler. It has individual flow check valves on the supply side and individual circulators on the return. One of the zones has constant heat even when the thermostat is off and not calling for heat. The pipe on the return size for that zone is hot. I already replaced the flo control valve for that zone and the output of the flo control valve is not hot. Any ideas?? It was fine previously. It’s zone 5 (top floor), the one with the green Taco 007, and the shutoff valve partially closed now to control the heat till I figure it out.

hot_rod

Is the pump for that zone shutting off? Is this a new problem?
In some cases you need to have a check on both supply and return.
Maybe add one in the green circulator to give you checks on both S&R.

Alan (California Radiant) Forbes

Are you sure that the weighted plug in the flo control is in the down position?

EdTheHeaterMan

Is that the original pump for that zone (only Green one in a sea of Red). I wonder if the old red one had an IFC inside it? IFC = Internal Flow Check
You may find what is going on in this text on page 9 https://www.xylem.com/siteassets/brand/bell-amp-gossett/resources/technical-brochure/fh-z100b-bg-zoning-made-easy-2.pdf. It is sometimes referred to as Ghost Flow. Also... what Alan is referring to is on page 8 of this booklet.

George_15

thank you for the replies! the problem actually just started last week. i had a frozen pipe and in the process of troubleshooting, I replaced the flo control valve and the circulator for this zone. the output of the flo control valve is not hot when the the thermostat isnt calling for heat. not sure if it's something with the taco 007 circulator, when all others are bell and gossett. the bell and gossett did not have a IFC.

EdTheHeaterMan

Interesting... something must have changed since it did not have this problem before the frozen pipe. So you have a new flow control valve and a new pump, and I assume some new pipe to replace the frozen section of pipe.

This does not make sense to me but I'll throw it out there. Is the Taco pump design more conducive to Ghost Flow that the NRF-22 from B&G? If it is Ghost Flow as explained in the booklet on page 9. then adding the IFC to the Taco 007 will correct the problem. https://www.supplyhouse.com/Taco-006-047RP-IFC-Replacement-Kit-for-Select-Taco-00-Series-Cartridge-Circulators

George_15

luckily, the pipe thawed with no damage. yes... something must have changed. the output of the new flo control valve in not hot so that should rule that out. that only leave the taco 007 which is on the return

EdTheHeaterMan

Do you still have the old red pump? Try putting it back. Just a thought.

Or if not, swap the green Taco with one of the Red ones and see if the problem moves with the pump.

hot_rod

The handle turned down all the way on the flo check?

George_15

yes.. the handle is turned all the way down on the flo check and the output of the flo check isnt hot. a little hard to believe that using a taco 007 when all the others are b&G would cause this

HVACNUT

Not sure about B&G, but Taco flo checks come with a piece of cardboard wedged between the weight and body. 

mattmia2

It is probably gravity flow with currents within the return pipe. The higher the emitter is above the boiler the stronger that effect can be. Maybe the shape of the volute on the b&g acted as a heat trap. You could put it back in and see if the ghost flow goes away. The fix is probably putting the ifc in the taco.