I'm not getting any cabin heat in my 2000 Insight. 3 weeks ago the heat disappeared for 10 minutes during a long drive but then came back on for the rest of the trip. After that the heat disappeared for longer and longer periods until now there's no heat at all. I've replaced the thermostat, done the burp procedure very carefully, checked the valve to the heater core (it works fine) and back flushed the heater core (there was no sign that the core had been clogged). The little motor that opens the valve to the heater core works fine--I can see it moving--and the blower works fine, just no heat. At this point I can't think of anything else I can do short of removing the heater core unit, which obviously I want to avoid since it involves first removing the dash. Am I missing anything? Is there anything else I can try before removing the heater core? Thank you for your time and your suggestions.