Siemens IQ700 Zeolith dishwasher SN26T297GB/93

I have a Siemens IQ700 Zeolith dishwasher – The one with the internal blue Emotionlight. The dishwasher works perfectly but the blue light is only working intermittently. I have plugged in another lighting unit from an older IQ700 machine and this also worked intermittently. What is the cause? – Is this controlled from the door switch? Could it be a loose connection? Before I dismantle this area to check, a few pointers would be useful. Thanks in advance.