[jeff5may]

Aha! In that case, I agree with Steve: something is not right. With a refrigerant to air heat exchanger as the condenser(heating mode), the discharge temp and pressure are much higher than a hydronic loop(cooling mode). This gives the dsh a higher ceiling to leech heat from in heating mode. If the unit blows good, warm air, the compressor discharge line gets hot enough to produce hot water.

The fact that you get less hot water in cooling mode is due to your latitude and the fact that you heat more than you cool. Your lower ground and loop temperatures outdoors are reducing your compressor head pressure. Also, the reduction in run time reduces your potential dsh output.

If your entering water temp is very low, the dsh may not see the water long enough to heat it up hot. For example, 45 degF water heated to 80 degF will have absorbed lots of btu's, but still not feel hot. If the dsh is recirculating through a large preheat tank, the heat gained will slowly raise the tank temperature while the heat pump is running. When incoming fresh water enters the preheat tank, its effects are pretty immediate unless you have the tank set up to stratify.

The entering and leaving water temp spread of the hx should remain fairly constant after the heat pump has run long enough to find its balance point. This would be the first parameter I would verify. As others have said, it doesn't take millions of btu's to heat up a single family home-sized tank of water. This can be easily calculated with the dT parameter of the dsh and a reasonable estimate of your water flow through the hx.