Discovery 2 td5 not getting hot

Hi all and merry Christmas

I have a discovery 2 which I’ve had about 4 months now,
The problem I have is that the temp gauge doesn’t go above 1/4 only when you go down hill it goes up to half way then back to a 1/4 when on the flat? the heater is nice and warm and there’s no pressure any where so don’t think it’s a head gasket

thanks Travis

Hi, seems like stuck open thermostat or air in the system, bleed it well first...if it was HG it would have overheated

Or a faulty sensor?