heater control won't go hot

[C2K]

Anyone had issues with the heater controls before? Wondering if swapping the control panel out might make a difference.

On my Rallye I can't seem to get the heater knob to reach all the way to hot. It seems to go to 95% but if you turn it to 100% then it often just springs back. Heaters are average at best, not really toasty. I can see that cable is ok all the way down from the control panel to the flap spindle (by bottom centre dash bolt) but i'm guessing it's spring return and is just overpowering the cable as it feels much the same if i push the flap lever myself. This started after I fitted a new matrix, but I can't see how i've put anything back in a way that would interfere.

Anyone got any photos of the heater box with dash out, or a car with no dash in atm they can help with pics?

Edit:

Just found a new one on ebay, can't see that the spindle passes through so obviously mine is sticky inside which isn't helpful really. Hot knob connects to the red arm on this pic