Aquahot issue

If it was working properly before the service, then I would suspect something done at the service caused your problem. MOST common item that would affect intermittent operation or NO operation on Diesel burner after the annual service would be they did something with the spark ignitor gap. Replacing the Fuel nozzle, you can easily disturb the correct gap and there is a tool mounted to the outer burner housing for verifying the correct gap. The gap should be checked AFTER the fuel nozzle is replaced. Also, when reinstalling the burner assbly, it is very easy to accidently hit the spark electrodes on the Aqua hot housing and cause a gap problem. Do you know what they ACTUALLY did on the annual service? Doug