Poor heating

[dreja]

Today I have completly flushed all the coolant out.
Then I've also washed the system, including heater radiator with pressurised water and there were no obstacles.

I've also checked the heating valve (the valve that opens the flow through heater) and it works ok.

Then I dismanted the thermostat (thanks to ZaX for the info about it location ) , and it seems it works ok. When I put it in cold water, both "caps" moved in the way shown on the picture...

I don't have any idea, what else could be wrong, because the heating is very poor, although there wasn't any air in the system...

Regards
Andrej