Q.There is a bubbling sound of air.

A.It is not abnormal. It is sound of air between fuel tank and fuel acceptance fitting goes in and out.

When you use the heater, the room temperature becomes around 20℃. However, once it extinguishes and room temperature decreases, the air inside the fuel tank gets cool and balance between atmospheric pressure changes and it causes bubbling sound when the air goes into the fuel tank. As the temperature slowly goes down, there is a bubbling sound for 1~2 hours. The cause of the sound is the change of temperature. Fuel acceptance fitting, which receives the fuel, has enough spaces, so the fuel does not spill out.