I recently changed the diesel filter and spray nozzle on our Aquahot. I did not fill the new filter before screwing it on. The instructions said filling the filter is not necessary but advisable because then the Aquahot would not require turning on several times to get the filter and lines to the nozzle primed. Okay, after a few times turning on the Aquahot, the filter was full of diesel and I could smell unburned diesel at the end of the exhaust pipe... so I knew the diesel got through the nozzle. If I remember correctly, if the fuel pump is not working properly, then it will not fill the filter and prime the lines to the nozzle.
The reason our Aquahot would not fire up was a bad control box... which I had replaced with a newer, black control box only several years ago. Well... now it has been replaced again and all is well. The Aquahot tech told me the older, original, silver control boxes are more "mechanical" while the newer style, black control boxes are more solid state... but the new style black control boxes are made with cheap components and have gained a reputation for being unreliable. I paid $150 for the service call plus $650 for the rebuilt silver control box.
I don't know what your device's problem is... could be the fuel pump, could be the control box, could be something else, but that is my recent experience.