Need help connecting radiant heat with tankless water heater

[DougNM]

I'm using a Rinnai tankless water heater to supply hot water to a bathroom and two sinks (600 s.f. studio) and radiant heat floor. I have hot water going to the bathroom and sinks but no hot water going to the radiant heat. I have a pump on the return side of the radiant heat but when the pump is running it does not activate the Rinnai. Should the pump be on the supply side and not on the return side? Will that help or am I wasting my time?

 

[DougNM]

Attached is a photo of my setup.

 

[breplum]

You should have a Combi unit. or add a boiler. It is not proper to have stagnant hydronic heat water mixing with Domestic Hot Water.
Combi units separate DHW via double wall heat exchanger built inside the unit.