Prius07 CHS system p1116, p1118, p1150, p1151

Hey guys,

About a month ago I got code P1116 "Coolant temperature sensor circuit stuck for CHS system".

I replaced the CHS sensor & cleared code, and drove it fine.

1 week later p1116 returns with a p1151 "coolant heat storage tank".

We checked the wiring to the harness on the CHS sensor and tested the sensor itself - both fine. There is also no damage to the CHS tank itself.

I continued to drive it around town and on freeway minimally - no overheating, running fine.

Then in addition to p1116 and p1151, I got the code p1118 "coolant temperature sensor circuit High for CHS system".

I tried bleeding the system both the CHS tank, and heater core. Significant air did come out of heater core, and multimeter reads 3.7 when jumping relay to CHS pump.

I cleared codes again and continued to drive minimally while monitoring coolant temperature. Again runs fine, no overheating.

Now it is only reading codes P1151, and P1150 "coolant path clog up for CHS system".

I should mention I'm currently at 155k.
At 150k I had 3 way valve replaced - but mechanic bled it improperly after installing. After discovering a radiator hose blown off, we clamped it back on, and I replaced coolant w/ prestone universal. I then later drained and refilled w/ prestone asian red. ( I was on a road trip and had to make due).

I'm thinking because the issue is persistent in CHS system, yet all parts seem to be functioning fine (CHS tank, pump, sensor) that there is some sort of crud causing misreads between the coolant temperature sensors, perhaps around that 3 way valve area.

I'm not familiar with flushing a coolant system, especially with a Prius cooling system. Does anybody have experience in this area w/ a 2nd Gen Prius revolving around CHS & 3 way valve flushing ..and does this seem like a good hypothesis for diagnosis of the issue?

Thanks for your help.