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