406 Hdi Warm Starting

I have a 1999 406 Hdi 110. Great car, fully serviced etc. However in May this year it failed to start from cold. The engine turned but would not fire up. After a succession of trips to a couple of garages the pump in the fuel tank was replaced (twice), the engine mounted pump and the air flow mass controller was swapped temporarily. The glow plugs are OK. Following this the car always starts but often after several attempts. It seems that starting a cold engine is not a problem, but starting an engine which was hot and then allowed to cool for 20 minutes is a problem. Starting a hot engine is OK.

Has anyone any suggestions where to look next?

Thanks

Check/replace the temperature sensor - look like it is temperature related.

Thanks

Is this easy to access and check? Where is it? How much approproximately to replace?

Cheers

remove the air filter for a day and see if that makes any diff.also they got sensors on the engines i bet one of them is playing up,good luck.