I have an in ground spa (elevated, with water fall into pool) attached to my pool. I turned on the heat pump last night to heat the spa and noted that my spa water level was slowly dropping. I ensured that all pool valves (vacuum, skimmer, return, main drain) were closed since I only have one pump for both pool and spa, and only the spa main drain was open. I then noticed leaking of water at the exit from the heat pump to the pool/spa return pipe. I shut pool pump and heat pump off (did not re-open the pool valves). This morning the spa had lost even more water (significant amount) although nothing was running. I do not notice any leaking at the exit of heat pump to return pipe when I have the pool return valve open. Could this be a bad spa return check valve? I just moved into this home and this is my first time attempting to use the spa and heat pump. HELP!