Robertshaw 710-501 Gas Valve 30067439-890 the heat relay sequencer is

the heat relay sequencer is likely the culprit

The Cleveland Controls NS2-0000-01 is a versatile differential pressure switch engineered for sensing air flow in HVAC and energy management applications

resulting in superior superheat control even under partial load conditions

These part numbers refer to the same technical component

Look for excessive corrosion on the burner ports

Robertshaw 710-501 Gas Valve 30067439-890 the heat relay sequencer isThe Robertshaw 710 501 Millivolt Gas Valve is a reliable low profile gas control designed specifically for space heating applications where space is at a premium. This non regulated Robertshaw valve features a 1 2" NPT inlet and a 1 2" NPT outlet, delivering a capacity of 150,000 BTU. Engineered for millivolt replacement projects, it functions without external power by utilizing the millivoltage generated by a standing pilot thermopile. The 710 501