Tankless goes lukewarm, Scratching my head... why?

[Toocutetofail]

Hello,

I was trying to diagnose a tankless water heater problem as the water would turn hot to lukewarm after few seconds. In the process, I wanted to make sure there was no hot-cold water crossover from mixer valves at any of the fixtures. So I turned the valve off at the outlet of the TWH (tankless water heater), turned on the hot side of washroom tap, water comes out for a little while and then stops. That's good. There is no cross over. However, I repeated the process for main level taps. Kitchen tap and washroom tap does not stop running. I can't figure out how cold water is crossing over to hot side. I closed the valves on all the other mixer valve taps.

I do have a recirculation line on the TWH but I had the cold inlet valve off on the TWH so there is no way recirculation line is adding water to the hot side.

I am so confused.

I would really appreciate if anyone can suggest anything to try.

thank you

 

[John Gayewski]

Is there a spray nozzle on the kitchen sink? Are the two that seem to be crossing over single handle faucets?