by Roger Berke
When you turn on the diesel heat, the diesel burner goes into a lighting sequence. The following things happen in this order.
The blower motor starts, which starts the fuel pump.
The motor runs for about 1 minute to allow fuel pressure to build up and stabilize.
The fuel solenoid opens (spraying fuel into the burning chamber), the ignition coil starts creating a spark across the electrodes (igniting the fuel that has been sprayed into the burning chamber).
There is a very slight delay. The photocell (that is adjacent to the burning chamber) looks for light from the burning diesel fuel.
If the photocell sees light, everything is good and the burner will continue to run.
If the photocell DOES NOT see light, the fuel solenoid closes and the `diesel’ light next to the switch in your coach goes out. The blower continues to run (purge cycle) for about 2-3 minutes to purge unburned diesel (and heat if the unit has been running).
Blower motor shuts down.
As you can see, this is a complicated sequence. If ANY component fails to operate properly, the diesel burner will not operate.
There is some troubleshooting information in the Aqua-Hot Service Manuals for your unit.
Some things that you can check:
Fuel – The fuel tank pick up line is like the generator, it will not pick up fuel if the tank is less than ¼ full. I have heard of coaches that won’t draw diesel if the tank is less than 1/3 – ½ full. You would know your coach better than anyone else if this is the issue.
It could be any of the following items that have failed. Fuel pump, solenoid valve, clogged nozzle, ignition coil (+wires + electrodes), or photocell. On the older (non-electronic control board) Aqua-Hot, the high limit thermostat.
You will be able to get at least some heat from the electric element. The electric and diesel systems are completely separate.