New set up. Old Modine 105K with LP conversion. Resideo valve w/standing pilot (all new parts), and new Fisher R622 regulators. Three 100 lb tanks connected to 3/4” manifold and 40ft 3/4” line to second stage regulator. Then 18 ft of 3/4” line to gas valve. Pressure gauge on manifold shows 75 psi at 40 degrees F outside. Second stage reg set to 11” wc at initial set up. Input pressure at valve measured at 11” wc drops to 6” wc when burner fires. Unit runs for 3 minutes, then pilot and burner shut off. Second stage regulator adjusted to 14” wc measured on valve inlet. Inlet pressure then falls to 8” wc when burner fires, runs 3 minutes and shuts down. When the system shuts down there continues to be 24V measured at the valve. There are no other appliances. Suggestions for how to proceed? What could be the cause for the pressure drop? I understand the inlet pressure should be maintained at about 10” wc minimum while burner is fired. Resideo manual says inlet pressure should be 12-14” wc but does not describe acceptable pressure drop.
source https://hvac-talk.com/vbb/threads/2243887-New-Old-System-Startup-Failure?goto=newpost
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