I have a grant vortex pro condensing boiler, 2 years old. From about October 2012 it occasionally cut out and the lock-out button light came on. The boiler started OK when this was pressed. The oil tank was full. The oil line filter is new. we have a remote thermostat for the upstairs radiators and a hot water tank heated by the boiler. The downstairs radiators have a thermostat. All the settings are as they were before this fault appeared. I had an engineer out to find the fault. He found none. He serviced the boiler, installing a new fuel jet. He commented that the inside of the boiler was very clean. This fault is intermittent and does not seem to have a pattern, cutting out randomly. Any ideas? Im not an expert, although I am a race car engine builder and understand mechanics. I think this is an electrical problem, is there some component that could have an intermittent fault, and if so, can it be tested with a multi-meter? I have one for resistance, voltage, amps. Thank you in advance and happy new year!