When troubleshooting, use soapy water. Find and stop ALL bubbles before you move on! Bubbles mean a loss of air pressure and reduced fuel delivery. These heaters are not tolerant of air loss! Period.

    Much time and money can be wasted if bubbles are ignored.

  click to enlarge

click to enlarge

 click to enlarge

 Don't take a short cut!

Use soapy water and stop the bubbles. You will be money ahead.