RV Doctor – RV Heating Flame Keeps Going Out

Dear RV Doc,

We own a 1999 Safari with the Hydro Hot heating system. The system will run for a while then the fire will go out causing a flame-out warning light on the panel to light. Sometimes it will go on and off like it’s getting air in the line. I’ve bled the line as per the manual but continue to have this problem. This makes for some cold mornings as the thermostat continues to run the zone fans without any heat coming from the radiators. Any ideas?
– Greg Peterson, (Bremerton, WA)

Answer:

Greg, Hydro Hot units are relatively complex in their operation, but I will list the most likely components. I would, however, recommend having your unit serviced at an authorized repair center.

Having said that, I suspect that your problem may be simple yet often overlooked. Although they are quite reliable, these units do need periodic maintenance. Even though the problems you are experiencing may be caused by component failure, it’s more likely that normal wear is the culprit.

Check the water/coolant level to make sure it is correct. Annual replacement of the fuel filter and fuel nozzle, in addition to cleaning the combustion chamber are required in order to keep Hydro Hot units operating properly. If either of these fuel components is clogged, dirty or otherwise faulty it could easily cause the problem you are describing.

You did not mention whether you have had regular maintenance and consumable replacement done on your unit, but the first thing I would do is replace both the fuel filter and nozzle. Check the fuel screen filter located in the fuel supply inlet of the fuel pump for dirt particles. Clean and/or replace if necessary. Also check for water in the fuel filter inspection bowl. As with all electrical devices, check all the wiring connections at the control module and elsewhere to make sure they are clean and tight.

We can check for air in the fuel line quite easily. First, ignite the burner and listen for a sputtering sound from the exhaust system. If there is a constant sputtering, then there is likely to be water. Clamp off and remove the fuel return line and attach a short piece of hose to the fuel return port. Place the other end in a container of diesel fuel and ensure that it is completely submersed in the fuel and then turn the diesel switch on. If air bubbles are visible in the container of fuel, inspect the fuel system (supply side) from the vehicle’s fuel tank to the diesel burner.

Inspect the fuel system for loose fuel connections at the Hydro-Hot and diesel burner, as well as the vehicle’s fuel tank and tighten if necessary. Also, check that all fuel filter head fittings are securely tightened. Be sure to check that each fitting at the fuel filter head contains thread sealant. A fitting without thread sealant could result in an air leak. Be sure to clamp off both fuel lines at the filter head prior to any fitting removal.

If fittings are removed and reinstalled, be sure to remove the fuel line clamps prior to attempting a heater restart. Failure to do so could result in serious damage to the diesel burner’s fuel pump.

It is certainly possible that other components could be faulty, but since the burner ignites initially before going out, complete component failure is unlikely. Possible culprits include the fuel solenoid, which could be sticking or otherwise intermittent, the control board, or the fuel pump. Less likely are the ignition coil, electrodes, flame sensor, and motor.

(Please feel free to comment, however, please also note that due to the volume of communications I receive from multiple channels I cannot guarantee a personal response in every instance. However, questions of an overall general interest may be considered and published in an upcoming RV Doctor column.)