16vt radiator fan (air con)

ok ive got a 16vt with aircon and i have got 2 fans. (only 1 working)
when driving my temp is fine.
when sat in traffic the temp goes very high at about 95 the fan kicks in for about 5 seconds but the temp doesnt go lower than 92 ish.
now am i right in thinking that if both fans come on then the temp would drop to 90 like it should?. now on top of all this the condition of my rad is about 70% ok. also i need a coolant sensor replacing (engine managment light is on)
but this light has been on for months now and the temp was fine so ive ruled that out. so i think its one of three things
1 radiator fan not working ( well one of them)
2 radiator condition ( although this is gradual and the high temp is instant)
3 or the thermostat ( but without both fans working i cant be sure)

the first thing i am going to do is check the rad fan might be a loose wire. failing that do i spend £115 on a rad which i will need in the future, or a new thermostat at £45 which is a right pain to fit.

any good advice would be great

just an update ive checked the fans today and they are both working. i think its looking towards thermostat?