2006 S Type 2.7D - Heating Issues - Advice welcomed

[RedAnt67]

I have recently bought a 2006 S-Type 2.7D. At first the heating would only blow ambient temp regardless of setting. So I have had the 3-way valve changed and now have a couple of different and related issues which are:

1. Heater will now give hot air BUT if you have completed any journey where the engine temp hits normal, when you start the engine again (unless it has been a long stop and the engine has completely cooled) the heater blows hot air - regardless of the setting - for up to 3 minutes before it drops to the level set. This happens every time. Suggestions on possible cause and remedy weclomed.
2. Having the air con on or off makes no difference to the output temp from the heater. I have not yet had the air con recharged or looked at as I wanted to resolve issue 1 above first but appricate that they could be connected?

Thanks in advance.