If the temperature is holding steady at 90 degrees the stat is working properly. If you have checked and bled the hoses, there isn't an airlock. If the car isn't overheating the water pump is running so there will be hot water in the system and the matrix in the car will be getting hot water.
Therefore, I would assume the problem will be with the temperature control flaps inside the heater box in the car. These direct air into the car over either the heater matrix, the AC evaporator or both in varied quantities to get the temperature to that required.
When the flaps stick, you will usually find that you will have not heat or full heat, depending on which position they have stuck in.
First course of action is to either disconnect the battery, leave it off a minute or so, then reconnect. That will get digital Clare control to re calibrate itself and hopefully will free off the flaps. After that its head in footwell time.
The flaps are controlled by individual motors. You should be able to hear then with the ignition on, but fans and engine off if you listen carefully.
If, when you move the heater control, you get a whir, click, whir, click kind of noise. That's the issue.