A flow switch 70 detects the movement of liquid through the shell 12 by testing for {HEAD ~ flow} in the shell liquid outlet tube 56 and prevents {TAIL ~ the burner} 16 from firing when there is no flow 
A flow switch 70 detects the movement of liquid through the shell 12 by testing for { HEAD ~ flow } in the shell liquid outlet tube 56 and prevents { TAIL ~ the burner } 16 from firing when there is no flow
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH