hi hope you guys can help me with this ive got a octavia 2010 diesel 1.9 tdi my temp gauge started going from 90 down to 50 and then back up 

the fan would kick in as if too hot then the eml came on error code p0118 coolant sensor circuit high

so changed coolant sensor got it from tps warmed car up with a drive round then temp gauge started going up and down again and eml light came back on 

put the blowers on to hot and i get hot air put blowers to cold and get cold air what i need to know is is my thermastat ok and could it be the water pump

any help would be greatly appreciated

You need to get the fault code read by someone with VCDS.it's possible it's the thermostat, look for any obvious water leaks.

the fault code is p0118  no water leaks but the fan does come on when heated up and temp gauge does go up and down

p0118 is an OBD code which is generic.

 

as post 2 said, you need to get the codes scanned with VCDS.  This should help pinpoint the issue better.