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