I have an oil-fired boiler with one primary circulator that feeds three heat loops, controlled by zone valves. 1st loop is indirect hot water tank, 2nd loop is hot-water baseboard, 3rd loop is to a set of in-floor radiant heat zones. The boiler aquastat is set to 180F high limit, 140F low limit.

The radiant loop is the issue - it should run at lower temperature, and uses a mixing valve to mix its own return back into the inflow to do so. Whenever a radiant zone is calling for heat, the current controls open the zone valve between that radiant loop and the boiler, and that zone valve tells the boiler heat is being called so it fires itself up to 180F. If radiant calls for heat for too long the whole loop overheats - the return water isn't cool enough to keep the temperature down and the whole thing runs away with itself. I've seen radiant loop hit temps of 150F, not good for the floors!

What I'm considering is installing an L6006C aquastat strapped onto the radiant outflow, set to break the radiant's zone valve when high temp is hit to shutdown flow of new hot water into the loop. That'd mean running the L6006C at 24VAC, not 120VAC.

Do you think this application would work, or is there a better tool for the job than the L6006C? Re-engineering the whole control system isn't an option at this point in time (future, perhaps!)

Thanks!

 

U can run an aquastat at 24 vac no problem.
very curious how a mix valve mixes in the setup you have.
I see no way for a thermostatic mix valve to operate with the circ before it as you have it.
Usually the infloor slab needs its own pump.

 

Yes... there absolutely needs to be another pump on the outlet of the mixing valve feeding the infloor tubing.

The radiant zone's valve should fire a two pole relay that simutaneously turns on the radiant pump, and at the same time the other side of that relay should fire the boiler and the system pump.

 

Guys, thanks for the responses and my apologies, there ARE additional pumps beyond the zone valve & three-way mixing valve, I just neglected to mention them. Here is the manufacturer's schematic (handily posted on my boiler room wall) which is pretty much a perfect match to the system.



I think the problem is the thermostatic three-way valve - by all appearances, the valve they installed in my system ISN'T thermostatic, it's just a plain old mixing valve!

 

Here's a picture of the valve, and I fixed the link in the other post (I guess it didn't like TinyPic, Flickr seems to work fine though).

 

I couldn't find anything on 'RTI' in a quick google search, but yeah, if that's not a thermostatic valve, it will temper the floor water, but not CONTROL it's temperature. As the supply water gets hotter on the inlet, so will the outlet. At some point, if it were to run long enough, the floor could get as hot as the boiler supply.

 

I think your system needs something else also... a Differential Bypass Valve.

When only one zone is calling, and in particular the radiant zone, your main system pump will be churning away trying to FORCE the water through the mixing valve.

A Differential Bypass valve would open and bypass some of the extra head (pressure) that the pump produces back to the return.

 

Here's where the DP valve would go:



I seriously doubt that you need that second air scoop on the outlet of the mixing valve. The one in the main loop is probably enough... but the second won't hurt anything, it's just redundant.

Unless the boiler manufacturer specifies that they want the main pump on the return, pumping into the boiler (some do), then the ideal location for that pump is AFTER the air scoop and expansion tank, on the supply side, ahead of the zone valves. It will work that way, but if you ever have occasion to do some repiping, move the pump.

 

The differential bypass is an excellent idea, thanks, and I should be able to put that in fairly easily as there's a disused loop available with the T's in all the right spots for that. I'll also look to replace the mixing valve with a proper thermostatic valve, but will still go with the aquastat solution in the meantime just to keep the temperature under control over there.

Thanks! Beer 4U2

 

So you would wire the R - B terminals on the 6006 in series with the call from your 4009 panel to the zone valve then?

I would make sure the model of 6006 you get has the adjustable differential. If you get one with the fixed 5 degree diff, you might end up 'short-cycling' the boiler.

You probably would want to try a setting of like 120 , and then experiment with the diff setting to find the best operation.