Ultimately to get all of these problems resolved requires a good read through the relevant section in the 944 workshop manual. Just today I completed a fix on my 968 to get the solenoid control for the feet heater output, the manual was very helpful because it has a mixture of diagnostic checks and pictures that explain things much better then we can on here. ISTR its section 87 which is in the Chassis volume. The heat control ultimately sends electrical power to move a solenoid which ISTR is the middle one of 3 on the left hand side of the heater, it moves the temp mixture flap and baffle flap (ISTR) up and down. If you get on your back under the passenger side of the dash you can see them. You can see the solenoid in particular and its assembly on page 433 section 87-58. To confirm that hot water is in the matrix you can just unclip the rods from the solenoid and move the linkages by hand. I did similar the other day for example to confirm that the output to the feet was OK and is in fact driven by the bottom solenoid. Section 87-62 on page 437 has the diagnostics checks to follow but it will only make sense once one becomes familiar with the various components. BTW I have one of those PITA vacuum hose problems yet to fix on the 968, the control for setting the system to recirc does nothing. Everything else works fine but when the recirc button is pressed I just get a faint whistling sound so either a pipe has popped of or is holed. Holding my hand by the blower inlet under the bonnet I can feel the same level of air blowing over my hand so I now the flaps are not closing. Lastly though if the heater worked fine before changing the coolant I would wager 9.9/10 times that its just an air lock in the heater matrix. I remember last time I bled the S2 it only bled completely after I could get the car on a slope so the bleed valve was nice and high.
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