My laptop's fan was pretty clean this time. So it was not a problem of dirty fan (as it usually is). But it was getting very hot and I had fan error message too.
I followed instructions from Lenovo service manual and extracted the fan from the motherboard. I wiped out former thermal paste that looked very dry to me and replaced it with new thermal paste (0.2 gr at each position).
Now the problem is solved for me. No need to replace fan or heat sink, or anything else.
I hope you find it useful.
Take care to clean former thermal paste thoroughly from heat sink and from processors and also to use the correct amount of thermal paste.