Trouble creating setpoint with user defined curves

From your description, it sounds like you have 4K as the setpoint limit for the curve you created. If you try to enter a setpoint that is higher than the setpoint limit entry in your curve file, the instrument will revert to that value.

You can verify this by selecting the curve entry button on the front panel and then selecting the user curve you wish to edit. Press enter until you see the Setpoint Limit Entry and change it to the value equal to or lower than the highest temperature you have on the curve. This will allow you to enter a setpoint up to the value you entered. Note, this is curve dependent so if you have more than one curve you built, you will need to modify all of them.