[bloo67]

the red triangle keeps coming on with the water temp light but goes right off but no heat. Replaced the thermostat it worked for about a week. I have a obdII no codes. Took to a shop they said 12V and hybrid 49% both replaced 3.5 years ago. Replaced 12V & hybrid was under warranty so it was replaced too. car has been fine for 2 weeks drove it about 1000 miles. yesterday the red triangle comes back on & goes right off. No codes no power loss but no heat. Anyone else have this problem?? thanks in advance for your feedback

 

[Easy Rider]

I think it should be fairly obvious that coolant isn't flowing properly in your radiator "loop".

It is fairly common to have water pumps fail on these cars but with a 20 year old car, it could be several other things too......like a plugged radiator or a collapsed hose.

Have you checked for pressure in the cooling system after it heats up ?

 

[powerliftingtexas]

5 years of Prius ownership I conquer with the above. I have yet to have a problem until this week and had similar symptoms start out as you. Than mine went to throwing all kinds of lights, red triangle, brake lights, exlimation mark, and all. There's not a lot break on these cars, but the inverter pumps do go out. I suspect your inverter water pump is bad. $27.00 on Amazon for a knock-off, $61.00 for a Dorman, or $85ish for a OEM grade. Your choice. From my research, 3-4 hrs to change your first time. 1-2 hrs your second time.

 

[punatechhybrid]

the red triangle keeps coming on with the water temp light but goes right off but no heat. Replaced the thermostat it worked for about a week. I have a obdII no codes. Took to a shop they said 12V and hybrid 49% both replaced 3.5 years ago. Replaced 12V & hybrid was under warranty so it was replaced too. car has been fine for 2 weeks drove it about 1000 miles. yesterday the red triangle comes back on & goes right off. No codes no power loss but no heat. Anyone else have this problem?? thanks in advance for your feedback

Coolant pump is going out. When it works, light goes out and when it doesn't work, Red Triangle comes on. It's intermittent and it is a common repair on Prius. $30 - $80 part. Fairly simple install, can be a tight squeeze if go in from top. Some good videos on YouTube. After install, refill and bleed air bubbles from system. Search again for YouTube videos on how to. Good luck