Newbie here, not great with mechanics but happy to have a go if it looks straightforward

My 2004 needs the coolant topping up every now & then, finally decided to do something about it rather than just top it up every few weeks.
I've noticed some dried spots of coolant on the radiator, so I'm guessing the rad's got a few tiny leaks in it.
I took the route of throwing some Radweld type stuff in yesterday. Put the back wheel on paddock stand & let it idle away in first to warm up & run it through the system,
Only it didn't move, it just sat there in the coolant tank.
I thought there have be a blockage in the hose, so took the side fairing off & took the radiator cap off. No blockage as the contents of the coolant tank started to empty out.
I was expecting to see liquid circulating back into the tank via the top hose, but nothing happened.
In traffic the temp soon get's upto 100 degrees (C), and the fan kicks in about 104. It never rises past this.
Once clear of traffic it soon drops back down again.
Is this something to worry about ?
I'm starting to think maybe water pump issue, or blockage in return pipe ? Although, I struggled to find the return pipe route to have a better look.
Would a water pump issue show up on TuneECU, I've plugged it in & no warnings shown.
Any advice appreciated.
Thanks
Paul (from Bolton, Lancs)