Hi I have a Glow Worm 18HXI in a Y plan with a Grundfos Alpha 2 and automatic bypass. Previously the setup was "simple". An ordinary room stat would call from CH and the circulation temperature was 65 to 68 degrees. Peace ruled. Looking for savings I installed the external temperature sensor, smart wiring centre and Climapro (software version 2.11). I have given up at present with the external sensor as house never seems to reach temperature. Anyway with the Climapro and smart wiring centre remaining I turned the circulation temperature up and when the circulation temperature reaches 74-76 degrees the boiler emits a noise/rumbling which can sound like a helicopter a little way away. I tried opening the bypass with no improvement. Turning the pump speed up to 3 (using the "traditional" 1,2,3 settings rather than the automatic ones) made things worse and the noise only eases disappears on speed 1 or setting the circulation temperature to 72 or lower.