RV Water Heater Pilot Flame-out

My water heater pilot light will not stay lit. I light the pilot and after a short time I am able to light the main burner. However it appears that when the water gets to temperature, the burner shuts off and so does the pilot flame. Any ideas?
George, (Artesia, NM)

 

Here are a few things to check George. First of all, be sure the LP delivery pressure is set correctly to 11.0 inches of water column pressure. My recommendation is to only allow a Certified or Master Certified RV service technician adjust the propane delivery line pressure. Plus I'm guessing it's time to perform a clean & service on the water heater. There are a couple things you can do yourself, however.

First, be sure the control valve is in the "off" position. Then disassemble the pilot burner assembly and be sure it is free from blockages. You can soak the pilot orifice in acetone or denatured alcohol. The pilot assembly itself can be cleaned using a common pipe cleaner after soaking. Allow the parts to air dry. Do not insert any item into the orifice and avoid using compressed air pressure. Inspect the flame spreader portion of the burner assembly and look for bent or damaged components. It must spread the pilot flame evenly in order to heat the thermocouple properly.

Remove and clean the large “J” tube or mixing tube and be sure it is free from blockages of any type, (check out the spider's nest in the photo above). The main burner flame spreader must also be centered in the opening of the “J” tube. Once the mixing tube is removed you can gain access to the main burner orifice. Soak and air dry this orifice also. The main burner orifice must be centered in this mixing tube when you re-assemble so take care to align the parts carefully. 

On the thermocouple itself, clean the tip using 0000 steel wool. Remove all carbon deposits. Re-assemble all components taking care not to over tighten the thermocouple into the gas valve. Just one-quarter turn past finger tight is all that is necessary. Check for gas leaks on any connection you disconnected and re-assembled using a soapy solution or an electronic leak detector. Be sure the soapy solution does not contain ammonia. 

If all checks out, light the pilot and observe the pilot flame as it engulfs the tip of the thermocouple. It should only impinge on the first 1/8-inch or so of the thermocouple. A too big pilot flame could result in pilot outage after the heating cycle. It would also be wise to have a Certified RV service tech measure the thermocouple output; it should produce a minimum 12-14 millivolts DC. A weak thermocouple output could also lead to pilot outage. If all the above tasks prove futile, the cause just may be a weak electromagnet or a faulty internal device called an ECO, both integral components of the gas control assembly in which case it will be necessary to replace the complete gas control valve.