First a Hello from a new member. I wondered if any of you experienced heating engineers have heard an intermittent whining noise coming from a new Vaillant ecotec plus 637 system boiler? Fitted (complete new system) June '16, S.Plan -two CH zones and one HW (unistor 210), external by-pass & TF1 fitted, flushed and commissioned as per tech. Has run like a dream until November '16 when, once a day at aprox 1.30pm there is for couple of minutes a whining noise from the boiler. Since then the system has be re-flushed and the by-pass adjusted, but the noise persists. Vaillant haven't answered my emails, so I thought I'd ask some real people, any pointers would be much appreciated. I have a video from the clients phone, but I can't seem to attach the file. Cheers R.