There are a couple things to try:

1) Freezing it to make the glue more fragile.

2) Inserting a thin blade along the edge and gently tapping until the heatsink separates from the processor.

Note that you want to go gently when you are doing this. A poster while back tried doing the latter and ended up shattering the CPU.

Im getting flashbacks of that other thread with CPU ripped in two 😁

Shponglefan wrote on 2024-06-28, 16:34:

1) Freezing it to make the glue more fragile.

Depends on the glue in question. It would work well for cement-like glue. If it's something like double-sided thermal sticky tape it would be better to get it hot (within reason, we don't want to damage the chip or get blisters on fingers) to make it "flow". Soaking overnight in 99% IPA might also help, at least soften the sides a bit, and it's safe for the chip. Solvents do next to nothing for cement type glues though.

I'm usually heating the heatsink to soften the epoxy/lessen the adhesive forces, and twist it off. Consult the absolute maximum ratings section of the datasheet for the particular CPU, it can safely be heated to its max storage temp. It's usually around 150 deg C for CPU:s in ceramic packages.

Clamp the CPU in a vise with aluminum or copper jaws. Use minimal force, just so it stays clamped. Heat the heatsink with a hot air gun, keeping track of the temperature with an IR thermometer (remember to do the correct emissivity setting in the thermometer, default is almost never matched to metal surfaces). Once you hit target temperature, slowly/carefully twist the heatsink off. Use a thick leather glove.

Maybe you can use the thinnest painters knife as a last resort. But I would prefer cooling it in the freezer in a bag and see if it breaks the bond.

I'd replace the fan instead, it's like $3.

Mandrew wrote on 2024-06-29, 10:31:

I'd replace the fan instead, it's like $3.

I have attached an image I uploaded to imgur of the cooler to my initial post and on it you can see that the fan is inset into the heatsink and is also the fan is moulded or glued to the heatsink meaning i can't easily replace it.

I had a Pentium Pro with a heat sink that was either intentionally glued on, or the thermal compound had solidified to the point where it was indistinguishable from glue. I let it sit overnight in the freezer, and the heat sink popped right off with some gentle prying. That trick has also worked well for me for several video cards that had petrified thermal compound.