Solved Cannot release hotend

That is certainly a good first step and if that sorts it you are finished
If not then you need to replace the thermistor. You don't need to disassembled the entire hotend for that, just loosen the setscrew on the heater block that holds the thermistor in place and replace the thermistor -- https://www.partsbuilt.com/r1-thermistor-robo-3d/

 

Yes, that is the thermistor.

On the R1 it will be just as your picture and is stuck into a small hole on the hotend heater block and there is a plastic/rubber boot that wraps around the heater block to hold it in place.

On the R1+ it is inside a small metal canister that is held in the heater block with a setscrew,

If you have the R1 and have lost the boot, you can use kapton tape to wrap around the heater block to hold it in place.

Orange is the heater core.

 

Kapton tape looks like this and trust me -- this would be 2 lifetime supplies

https://smile.amazon.com/RETERMIT-Resistant-Sublimation-Temperature-Polyimide/dp/B07MM38WLP

 

Well there is a simple solution.
If the thermistor will go in, but the screws will not tighten on it -- use kapton tape to wrap the heaterbock and hold everything in place.
That is a special high-temp tape and it will work fine. You only need a couple of wraps to hold it.

You do it the way this picture shows although really you only need a couple of wraps around the block. Not quite as much as they show

 

If you have issues, open a new thread and we will handle it