# LP Systems and Certification Gated Work How a two stage regulator works, what a timed pressure drop test actually proves, how direct spark ignition appliances fail, and which LP tasks require a certified technician. ## How the System Is Staged Liquid propane leaves the tank as a vapor at tank pressure, which varies with temperature and can exceed 150 psi on a hot day. A two stage regulator brings it down in two steps: the first stage drops tank pressure to roughly 10 to 15 psi, and the second stage delivers appliance pressure at 11 inches of water column, measured with a manometer rather than a gauge. That final number is the specification every appliance in the coach is designed around, and it is not adjustable by feel or by ear. Regulators age. The internal diaphragm is a rubber component that hardens, and a regulator that reads correct at no flow can sag badly under the combined load of a furnace, a water heater and a range burner running together. Service life is commonly quoted at eight to twelve years, and replacement regulators are inexpensive relative to what a low pressure fault does to appliance behavior. On cylinder coaches the automatic changeover regulator adds a second failure mode: it stops switching between cylinders and the coach simply runs out. ## The Timed Pressure Drop Test A timed pressure drop test is the only honest answer to 'do I have a leak.' The system is isolated at the tank valve, pressurized to a specified test pressure, and watched on a manometer for a defined interval with no appliance drawing. Any measurable drop over that interval means the system does not hold. Soap solution on fittings comes afterward, to locate what the test already proved exists. Doing it in the other order finds the obvious leaks and misses the slow one behind the water heater. A drop that falls partway and then stabilizes usually means an appliance valve seat rather than a line. A drop that never stabilizes means a fitting, a flare, or a chafed copper line where it passes a frame member. Old flare fittings that have been broken and remade several times are a common culprit, as are LP lines routed against a slide out mechanism where thousands of cycles have worn a groove. The test is documented with the pressure, the interval and the result, and that document travels with the file. ## Ignition and Combustion Faults Most modern RV appliances use direct spark ignition rather than a standing pilot. A control board energizes a gas valve and fires an igniter, then looks for flame confirmation through a flame sense electrode. No confirmation within a few seconds and the board locks out. That single sequence explains nearly every complaint that starts with 'my furnace clicks and quits.' The failure is usually sense electrode contamination, a bad ground, insufficient gas pressure, or a sail switch and blower that never reached the airflow the board requires. Suburban and Atwood furnaces, Dometic and Norcold absorption refrigerators, and Truma and Suburban water heaters each have a documented sequence with measurable checkpoints. Diagnosis follows the sequence with a manometer and a meter, checking gas pressure at the appliance under flow, verifying the ground path, and reading microamps at the flame sensor. Absorption refrigerators add their own path: a blocked burner tube, a soot fouled flue, or a cooling unit that has crystallized and needs replacement rather than adjustment. We say which one it is before ordering parts. ## Why the Work Is Gated LP work is certification gated because the failure mode is fire. A technician performing LP line repair, regulator replacement, appliance gas valve service or a pressure test on a coach at OCRV Center holds LP certification, and the test result is recorded on the file. Refrigerant work on rooftop or basement air conditioning is separately gated under EPA 608 certification, because recovering and charging refrigerant legally requires it. Structural welding on frames and slide rails requires a certified welder, and ADAS calibration on newer chassis requires documented procedure and targets. The practical consequence for you is scheduling, not paperwork. Certification gated tasks queue behind the certified technician's availability, so an LP pressure test plus a Suburban water heater gas valve replacement does not compress into a same day service window just because the labor time adds up to two hours. Systems work runs 3 business days to 2 weeks for this reason. The hazmat and disposal charge of $45 applies flat when LP is purged or refrigerant is recovered, because both leave the building through a documented waste stream. --- Source: https://ocrv.club/guides/lp-system-safety-and-what-certification-covers OCRV Center, 23281 La Palma Ave, Yorba Linda, CA 92887 Phone (949) 799-3387. Email info@ocrvcenter.com. Serving Hacienda Heights and the surrounding area. 18.4 miles, 24 to 38 minutes via SR-60 west to Fullerton Rd, then south to La Palma Ave. In shop work only. All estimates are priced and credited against an authorized repair.