Took civic in had the cooling system flushed and thermostat replaced. Now it won't heat up. When stitting at idle will eventually get to 9 bars then as soon as start driving it will drop down to 5, 3, then 1 or 2. The top hose stays hard like a lot of pressure is building and bottom hose is pliable. Took it back and after 2 more thermostats (last one Honda original) a dye test, pressure test nothing same results. I'm lost and so is mechanic. Could this be the water pump? It does circulate when checked sitting in shop. This a one owner car and the first time it has had the coolant changed (85,000 mi). Help!

 

Did it work properly before taking it in? Maybe there is still air in the cooling system? I can't imagine all the thermostats are bad. Unless the mechanic is getting the wrong one for your car.