Sell it bro, your life will become so much easier. Its a fact that CNG totally messes up the upper part of newer engines... It results in overheating and eventual premature death of the motor. In short you spend trying to fix more than what you have saved(counting the cost of hassle as well).
Unless you have a suzuki Hi roof which does 100 km a day, CNG doesn't make economical sense.
A friend of mine has same model of civic with almost equal number of miles and maintained the same way, the cng wali civic now runs with direct fan and has had its radiator serviced a few times. The engine is a lot of noisier and idle is not perfect. On the other hand, my civic still starts, sounds and runs like a brand new car. It has never been overheated and the radiator or other components never required service. We connected OBD II monitor on both cars and ran under the same conditions, the CNG wali civic even with direct fan eventually gets much hotter.
I have gotten used to the price of petrol and now its a permanent part of my budget.