Heater problem

I hope by posting this problem again, someone can at least give me an idea what I must do. I really don't have the money to let Toyota dealers to run diagnostics and not finding out where the problem is

I have a 04 Prius. 200,000+miles .. yes..200k+ All parts on the car are original (except all four shocks) I am still consistently getting 48 to 56miles per gallon of gas. Because I couldn't trust anyone to change my coolant, I have never done it.

Recently my check engine light came on.. I suspect it is the PCV valve getting stuck (never changed) because the engine oil seems to be burning off fast.. because the PCV valve is hard to get to (behind cylinder #4 under the wiring harness for spark plugs and injectors), I will try to find a lift and change the valve from below of the engine compartment.

While checking for the emission leakage, I cleaned the air intake and though it would be a good idea to keep the engine running for a while. I remembered reading somewhere I must run AC at MAX to keep the engine running continuously.. Well, I did that but the engine still stopped.. so I though maybe I remembered wrong.. I then switched to MAX heat and this is when I discovered I had none. (The engine was hot when I did this) It is not the thermostat because I don't even have a bit warm air coming out at MAX heat setting.. the air from the blower is the same as if I turn off the ac compressor and just letting the fan blew in the cabin.

This past winter, my Prius' heat worked perfectly except a bit noise coming from the electric (aux) water pump... I recently noticed a couple of 'pink' spots around the water pump (no noise at all from the pump).. can a bad water pump stop the heater from working all together?? Maybe some worn out pieces from the water pump blocked the heater core? Any Idea?

Thanks ahead for any help!