BURP
The airlock is in the freshwater system from the hoses from and back to the thermostat from the hot water heater. It's called "burping" and there are two ways to do this: run the engine, experience extremely high temperature and crack open the little valve on the top of the thermostat while revving the engine (not recommended); or, either disconnect the hose from the base of the thermostat and use a Jabsco Par hand pump to assure that the water line from the thermostat to the heater is full OR just disconnect the hose at the thermostat and pour water (distilled) into it to assure that the air "bubble" is gone. I do that latter, it's the easiest. You can use our C34 message board and do a search on "burp." If you take the hose off the thermostat and fill with the funnel and water, you know you're finished when water comes out of the nipple under the thermostat where you removed the hose. Then just reattach the hose.Do an archive search on "burp" or "burping" to read more.