[pHaestus]

you really need some more technical specs of the chiller. When you say 150w cooling at what coolant temperature? If it's 150w at -20c coolant then something's dreadfully wrong. If it's 150W max cooling (resulting coolant is room temperature) then everything's working fine and your chiller's just maxed out.

I assume it's the latter and I can't understand why you expect something more out of this unit? Simplify the system in your mind: You are putting only slightly less heat in than the chiller can pull out so water temperatures should end up slightly below room temperature if you run the unit long enough to reach equilibrium,

You're going at it from opposite side of equilibrium (no heat source and all chilling then apply heat) and so it looks like the chiller isn't working.

Of course the unit could need a charge or something it's hard to know without more specs.