I have a K machine that is driving me crazy! Leaking (pulsing)out the vent tube during heat disinfect. Only happens when the machine is over 80 degrees C and the water is circulating through the system. All pressures are good. Looked at the deair and flow motors, valve 41, 30, 29 and 39. All seem good. Also checked heat exchanger and that was fine. Hydroblock and float switch are good as well. I am out of ideas. Any suggestions?

When you checked the exchanger did you open it up to look for pinholes? Or did you just look to see if it was leaking from outside? Also, could be actuator board/cable. And you are absolutely positive the float isn't sticking???

This is usually caused by heat exchanger. By-pass it and run H.D. again, see what happens. keep us posted

The shield is cracked in the heat exchanger. Replace and you will good to go

Updates on this?

It was the heat exchanger. Thanks for all of the help everyone.