Ghost flow help please

Isolating which valve stops the gravity flow? the supply, return or both? Believe it or not water can circulate (thermosyphon) through a single pipe without a direct return path. what's going on with the tankless coil that's not being used anymore right? maybe would help to set up the boiler for a cold start?

A Spring Check on the return should solve it. I've seen it even using all IFC circulators. I'd replace the internal check, and the problem is still there. And coincidence or not, they've always had Speed Headers. Yours in only using one on the supply. The zone usually effected is the one next to the indirect.

All circs would need the same check, not just the over-heating zone.

Boilers with tankless DHW coils are hot all the time and those can and have worked with flow checks, something is not adding up here.

At some point you get weary of the troubleshooting quest and just change to a different check.

I believe the checks used in circulators ICF, are .35- .50 psi pop. So they could in fact be less pop psi than what those flo checks are? But there spring assures that they do in fact close.

I don't see a spec at B&G or Taco for the "pop" of flow check. It would be equal to the weight of the plug if the opening it closes is 1 square inch.

If closing the valve to the return on the affected zone stops the "ghost heating" then to me it's pretty apparent there is thermosiphoning through the return, i would then simply add a spring check. Also as @bjohnny has stated look at the low limit settings on the aquastat control if your not using the tankless coil and have an indirect you shouldn't need to be keeping the boiler hot and i would suggest operating the boiler as a cold start..

I would narrow down which valve stops the ghost flow.

Is the valve downstream of the circulator and flow check?

Or is it the valve on the return piping?

Don't turn off both at once to determine the flow path of the ghost.

That will answer where a new check may be needed.

@plumbworker astutely noticed was your boiler appears to have a tankless coil in it. Presumably this was used before the indirect tank was installed. When these tankless coils are used, it is common to keep the low limit temperature setting of the boiler higher than what is truly needed (even through the summer months). So, even though, you are no longer using the tankless coil, the aqua stat settings may not have been adjusted to accommodate the upgraded & efficient indirect tank.

read through this tread, and the only thing that changed was adding 5th zone for DHW. It’s possible you’re creating a higher differential pressure overcoming the .5 psi to open check and allow flow into that zone. What negates my theory is it would happen in your other zones too. I like Hot Rod’s suggestion to take the power off the circuit to validate the thermostat. You can call Taco at 401-942-8000 for support.

But if the supply check is not, you could have 2 directional flow, heat going up and cold coming down the same pipe. So a return check still may not solve the problem. A graphic of that concept.

As silly as it sounds or looks we have had instances where we are told only a zone valve after the pump has corrected a ghost flow??

If true I would rip, out all the zone pumps and use a single delta P circ and zone valves. Cure the problem and reduce energy consumption 50- 80-% Most zoned pumped systems are way over-pumped anyways. 007's moving 1 or 2 gpm as example

Yeah, I'm still not clear if this means just turning the valve off on the supply after the flo check stops flow? If so the flo check, must not be holding. Which is very odd, to me?

Any chance you installed that Zone 2 pump backwards? Which way is the arrow pointing on the volute? It looks correctly oriented from the pictures but I cannot say for sure.

And this is with your boiler already hot at about 170 to 180F. So you confirmed it is thermosiphon effect. And the thermosiphon requires the entire zone loop. Did any of the other zones get hot past their Flo Chek?

If it was my house, depending what the high & low temp limit are set to, I would try reducing each of them by 15 degrees to reduce the thermosiphon forces. It sounds like your heat emitters have plenty of output to accommodate a lower temp. You can easily change the settings back.

So you just replaced the internals of the flow control i'm i correct? maybe the valve body has pitting or corrosion at the seating surface? If so maybe then consider replacing the entire flo-check if you haven't already?

Be sure to disassemble and inspect inside

The could be a forging or machine flaw. Maybe the plug doesn’t seat properly. There should be some seal marks on both pieces. The slightest of opening allows flow through