Radiant floor tankless boiler turning off

mattyt1984

I have installed a Tagaki Junior tankless water heater.  The problem I am having is due to a subfloor that is too thick over 2 inches with 5/16 pergo on top of that.  The heater and pump will kick on but after a while the heater turns off due to too high of an inlet temperature.  I have it set to 140 degrees which is as high as I can get it to go in hopes that the higher temp may push the heat up thru.  Any ideas of what I can do to get the return temp lowered when the inlet temp becomes 130 it shuts down?  I have tried lowering the flow rates with no success.  I was thinking of having the water return thru a radiator with a fan and adding in a hot air vent.  Any other suggestions?

Ironman

I'm Afraid...

That you're experiencing the reality that there's no way of overcoming improper design and installation other than re-doing it correctly.



The Takagi is not a boiler, it's a water heater - as in domestic water. It's not designed or controlled to take the place of a boiler despite all the Internet peddler's and quasi supply house's claims to the contrary.



How is it piped? Can you post some pics?



A wood floor should never see water temps above 140* and that's too high in almost any case. Can you give details of the construction of the floor, the tubing layout, lengths, etc? Were radiant plates installed?



More info, please.

NRT_Rob

not a useful way to think of this

most heat sources will cycle on and off during a heat demand. If you are not keeping up the problem is not that your heat source is cycling, it's that you don't have a strong enough emitter. Not that a takagi is a good choice for a radiant heat source, but hey, you already own it, so that's water under the bridge.



step 1 is knowing your heat load

step 2 is knowing whether your emitter can meet that heat load. If it's not, you already know that.

step 3 is knowing how to make your emitter meet the heat load. adding radiator, adding plates, adding insulation, raising water temps are all options if you are deficient. But if you don't know the heat load you're trying to hit, anything here except "add insulation" if that's deficient is guessing.



If you have any real heat load a joist system will probably want heavy gauge plates and good downward insulation (as in, real R value) to operate under 140. but even that may not be enough if your load is too high.

Gordy

Floor surface temps?

Obviously the floor output is not enough to meet the load. Just wondering what your floor surface temps are. It says a lot about where the heat produced is going, Back to the waterheater, to the space below etc. As Rob stated need to know the heatload of the space trying to heat. Pushing through an R2 worth of flooring is a lot of resistance.



Gordy

CMadatMe

Design

I'm on the same boat as the others. Need to take a step back and look at the entire system design. What is the heat loss? What application did you use for installing the radiant? With plates no plates. Define 2" floor, what's in those 2 inches?