Heater only blows cold

Our NZ (and JDM) Prius do not have the coolant control valve. That is associated with the coolant heat recovery system which we don't have.

Have you checked that coolant flows to and from the heater core freely?

 

Our colleague, Bill Merchant, on post nr. 4 in this topic says something about a fuse...
Did you check it?

 

The blower runs, right? It blows air, just the air it blows isn't hot?

If so, the blower fuse is ok.

The small electric heater elements make a barely noticeable difference; they are only 700 watts worth of heat, compared to 5300 watts worth extracted from the hot engine coolant. There is probably nothing wrong with them and you would probably not be able to feel the difference if there were.

With the engine up to temperature and a demand for heat, have you felt the hoses to and from the heater, in the engine compartment? If the 'to' hose is hot, the hot coolant is circulating. If the 'from' hose is equally hot, the coolant is circulating through the heater without having much heat extracted.

That would only mean the air being blown by the heater is not passing through that core. The heating temperature is regulated by a movable door that determines how much of the air goes through the core and picks up heat, and how much goes around the core and does not.

There is a switch and actuator check mode for the heater that can let you command that door to various positions and confirm it goes there (or just running the heater and changing the temperature setting from max cold to max hot should have that effect too). If the actuator doesn't move, there's the problem. If the actuator moves but the air temperature doesn't change, the door is broken inside the heater.

If the actuator moves and changes the air temp when you explicitly command it, but not in ordinary operation, the cabin temperature sensor might be flaky or disconnected leaving the ECU to think no heat is needed.