Freezer temp is fine at -22 but fridge is to warm at +18

Refrigerator temperature may also change due to the door being opened too often, someone else changing the temperature settings. It could also be caused by a failed electrical component.

adjust the temp on the freezer setting where it links up with the frig'...

fridge temp should be 30 to 35 degrees/freezer -1 to -5 f or between 2 to 5 C for fridge and -18 to -22 C for freezer several times a day is too often...... try once every 2 days without opening door in between checks....

My miele fridge freezer has just come up with a fault code F4 where the temp is... what does this mean and how can we fix it???

Check the back wall of the freezer compartment for ice buildup. Sounds like you have a defrost issue.

freezer temp should be set to approx -18 to -22 degC
fridge should be set to +4 to +6 degC

seems like its not defrosting in the fridge. remove rear panel and look for ice around the thermister.

Sounds like a main board problem cause the temp should not be accurate one minute, then way off the next. I would have someone look at this cause it would be difficult to figure this out without being there to troubleshoot it

It sounds very much like control board problem. The chances of both sensors at fault seems unlikely. Unusual that it is the exact same temp unless they are your setpoint requirements. I would advice contacting reliable fridge guy to check the cabinet. Hope this is of some if not much help.