Hi, I have an external Grant Euroflame Oil boiler with Riello RDB burner. Recently it has started to lock out occasionally but then be okay for a while. Having not had it serviced for a number of years i decided to get it serviced. The combustion chamber was cleaner out, nozzle changed, pump pressure and emissions checked. Worked fine for a day or so and then locked out. Pressed reset button and took a few attempts but did fire up, but then within the hour it had locked out again. I reset again and same thing happened. Now it just won't even begin to fire up. I press the reset button and it buzzes for a while, then clicks and makes a louder buzzing and then resets again. Can anyone help? (We have plenty of oil) Advise very welcome as I'm so fed up with this boiler now. Thanks in advance!