Even with heater off sits at 90 but when it's on it blows hot

Ah right so it just sits around the 89 degree mark all the time? I'm assuming that is with your heater on? It may just be the time of year. Corsa temp gauges do seem to move about more than any other vehicle I've driven so that probably just makes it more noticeable that something seems different when in fact it's just that the cold weather means you're using your heaters more and the cooling effect on the radiator is increased.

When my stat went the temp gauge would fluctuate between the first mark and the 90 degree mark depending on what speed I was doing. Around town it would sometimes just reach 90 but when I got upto motorway speeds, it dropped down quite a bit and the heater worked less well. I assumed you were in the same boat but after you saying that, I'd say your cooling system is probably working quite efficiently.

it gets warm at 89 but then it doesnt move on the dial

I'd say so yes. I can't think of another explanation as to why that pipe would only be warm, it should stay cold until the coolant in the block gets to 89 degrees then the thermostat opens and the pipe quickly goes from cold to hot.

so is a new thermostat required still?

Thermostat is probably stuck open. It happened twice on my 1.2, the coolant just flows freely so the hose will warm up but with the cold weather, it can't get hot.

Pipe get warm so it's not the thermostat

It's on the righthand side of the block. Follow the top hose from the radiator and it goes straight to the stat. It's easy to change, disconnect the hose then there's 3 torx bolts holding it on. You'll need the gasket too, they usually break when you pull the stat off.

Hello anyone know where the thermostat is on a corsa b 1.2 16v and how easy it is to change
My cars been sitting under 90 degrees constantly no matter on how much I rag it or how far I travel

Thanks