Problem with hot water tank that is used also for space heating

[curt1s]

Hello,

Below is a picture of my plumbing setup with my hot water tank, which is also contected to my space heating unit:

The problem with this setup is that even without a mixing valve, and the thermostat on the hot water tank set at maximum hotness, the hot water in my showers does not get hot enough. What I did discover though is if I shut off the two valves going to the space heating unit (circled in blue), then the water in my showers is very hot. Are the pipes in this setup somehow wrong? Should the pipe going to my space heating unit go upward instead of downward or does that not make a difference?

Thanks!
Curt

 

[phishfood]

My guess is that the check valve in the space heating unit is not sealing, and when you use the shower, it draws cold water back through the space heater and mixes it with the hot water coming out of the water heater.

Adding in an external check valve should fix the problem, though if the space heating unit is still in warranty I would try to get it repaired.