Flame outage on non-vented LP heater? Here's help

If you have a non-vented propane heater in your RV, like a 'Blue Flame,' a 'brick heater,' or even a catalytic, there are a couple of important pieces of safeguard equipment on your heating unit. The first is a pretty common one – a thermocouple, which "reads" the standing pilot light, and shuts down the gas valve if the pilot should go out. The second is a clever little gadget called an oxygen depletion sensor (ODS). This "reads" the available oxygen content in the room air, and should the oxygen level fall below a given point, likewise shuts down the heater to protect occupants from asphyxiation.

These two safeties are tied together, and if either one should fail to work properly, then you'll know the misery of a cold morning when you can't get your heater to start, or to stay lit. Since they are related, it can be difficult to discern which of the two safety devices is in need of attention.

First, a bit on the principle of operation. The thermocouple ("A" in the photo) is a clever device that when heated by the pilot light, produces a small amount of electrical current. This current is passed along to the gas valve, and as long as there is sufficient voltage, holds open a valve, allowing gas to flow. If the pilot should go out, then current is no longer produced, and viola, the valve slams shut, halting the flow of gas.

The ODS ("B" in the photo) is an integral part of the pilot burner. The little hole (to the right of the "B" arrow point), called by some manufacturers the "pilot air inlet hole", is the critical point of the safety. If insufficient oxygen flows through this hole, then the pilot flame will tend to lift up and away from the pilot burner, moving away from the thermocouple. As the heat to the thermocouple decreases, you guessed it, the voltage produced by the thermocouple is reduced, and wham! the gas valve slams shut.

Regular maintenance keeps everything moving along nicely – or so they say. About every three months or so you should ensure the pilot air inlet hole is free of dust. A can compressed gas, such as used for cleaning computer keyboards, works great. A quick blast blows away the dust. In a pinch, put a drinking straw up to the hole and blast away with lung pressure.

But other things can hinder the operation of these safety devices. In the picture you'll notice that the thermocouple bulb is not encircled in flame. The pilot air inlet hole had been thoroughly cleaned, but the flame just isn't "cutting it." The heater would operate for a few seconds to even a minute or so, but then, boom, the pilot flame would go out, and the owner could hear the "click" of the gas valve shutting. What was the problem? If the culprit were reduced gas pressure, then there would be a telltale – a "lag" between when the call for main burner to operate, and the actual lighting. In this case, the main burner would flare up immediately on demand.

In this case, the weak pilot flame was caused by an obstruction of the pilot orifice – the point where gas enters the pilot burner. Look to the lower right corner of the photo – you'll notice some threads below the pilot burner. This is where the pilot orifice screws into the pilot burner. Shut off the gas to the heater, disconnect the gas line running to the pilot light orifice, and then unscrew the pilot light orifice from the pilot burner/ODS assembly. It'll take a couple of end wrenches, but it's easy.

With the orifice removed, sit it down over the top of a flashlight and see if you can see light coming through the orifice – chances are it's clogged. A shot of compressed gas should clear the obstruction. Stubborn obstructions may respond to a little rubbing alcohol and a wooden toothpick. Don't try to use a wire or other metal object – if the orifice is enlarged, you may have real problems. A worse-case scenario is if you can't clear the crud, you'll need a new pilot orifice, which is an inexpensive item.

Put everything back together in reverse order. Allow gas pressure to the pilot burner/ODS assembly, and check for gas leaks with a leak detecting device or soapy water. Free of leaks? Test fire your unit – and happy winter warming!