I only say that as when I changed my thermostat and re filled the system it took a long time for me to get the air out, thought I had done it prior to a pod run out and on the way home the temp started to hit the roof even with my electric fan, when I let it cool in the services most of the rad coolant was gone, presumably through the system. Topped it back up fully and it's now fine. Just set the heater to full heat, fan on highest setting and it should draw through. Then let it cool and leave the rad cap off, then check it again before the next start up. Fingers crossed. Like I say I am not a guru, and I am sure when the droves get back from the nec there will be more advice. Pete