LP gas
A guided diagnosis for RV techs. Each step is a check, a reading or a question.
- What is the LP complaint? Every gas appliance on the coach shares one regulator. If more than one appliance misbehaves, start here, not at the appliance. Expect: 11 in WC at the appliance under load. Lock-up (burners off) that holds steady and doesn't creep past about 14 in WC.
- Is there gas at the cylinder, and is it getting through the regulator? Check the cylinder level by weight or gauge. Then put a manometer on the stove manifold (or an appliance test port) and open one stove burner. Expect: 11 in WC with one burner lit
Causes and repairs
Out of gas
Refill. After a refill, air in the lines makes appliances take several tries to light.
Tools: none
Purge air by running a stove burner until it lights and stays lit, then cycle the other appliances.
Excess-flow valve tripped or regulator failed
Opening the cylinder fast trips the excess-flow check in the OPD valve; you get a trickle. Or the regulator diaphragm failed.
Tools: manometer
Close the cylinder valve, wait a minute, open it slowly a quarter turn, then fully. If still nothing with the manometer on, swap to the other cylinder or a known-good regulator.
Supply is fine, the appliance is the problem
11 in WC under load at the stove means the regulator and cylinder are doing their job. Go to the appliance that won't light.
Tools: none
Follow the Furnace, Water heater, Fridge or Stove guide.
Low regulator output
Under 10 in WC with one burner is a regulator going soft, a nearly empty cylinder on a cold day, a restricted pigtail, or a partially tripped excess-flow valve.
Tools: manometer
Reset the cylinder valve slowly. Try the other cylinder. If still low, adjust (if adjustable) to 11 in WC or replace the regulator. Regulators should be replaced about every 10 years anyway.
Pressure sags with several appliances
Fine with one burner, drops under 10.5 in WC with the furnace and water heater also on: the regulator can't keep up, the cylinder is low and cold (vapor can't boil off fast enough), or a line is undersized or kinked.
Tools: manometer
Manometer at the farthest appliance with everything lit. Replace a regulator that sags. Fill the cylinder. In cold weather a near-empty cylinder can't supply a furnace.
Stop: gas smell
Shut the cylinder valves. No flames, no switches, ventilate. Then find it.
Tools: electronic leak detector, bubble solution
Leak detector or approved bubble solution on every fitting from the cylinder in. Then run the timed pressure drop test (see the test branch). Repair and retest before you turn the gas back on.
Regulator freezing or vent blocked
Frost on the regulator body is normal when drawing hard. Frost plus loss of pressure means moisture in the gas or a regulator on its way out. A blocked vent (mud, ice, a nest) stops the diaphragm from moving.
Tools: manometer
Clear the vent (it must point down), install the regulator under a cover, drain water from the cylinder if the supplier contaminated it. Replace a regulator that keeps freezing up.
Using too much, or a leak
A furnace alone can burn a 20 lb cylinder in two cold days (30,000 BTU/h is about 1.4 lb/h). If usage doesn't explain it, leak test.
Tools: manometer
Do the math on the appliances first. Then the timed pressure drop test.
Timed pressure drop leak test
The test every tech should do the same way every time: 1) All appliances off, pilots out, every burner knob off. 2) Manometer on the stove manifold (remove a burner cap and use a spud fitting) or an appliance test port. 3) Cylinder on for a few seconds to charge the system, then off. 4) Open a burner valve briefly to bleed down to 8 in WC, close it. 5) Wait, then time 3 minutes. No drop means no leak. Any drop is a leak: find it with a detector and repeat.
Tools: manometer, leak detector
8 in WC held for 3 minutes with no movement. Also check lock-up: with the cylinder on and all burners off, pressure should rise to 11 and hold, not creep up past about 14 in WC (a creeping regulator is failing).
Auto-changeover regulator shows red
Red on the indicator means the service cylinder is empty and it has switched to the reserve, or the lever points at an empty cylinder. If both are full and it's red, the changeover stage failed.
Tools: none
Flip the lever to the full cylinder; indicator goes green. Both full and still red: replace the regulator.