Hi there i have a gloworm 30 hxi boiler. I had the time clock, room stat and cylinder stat changed 6 months ago when i moved in. The setup before did not let you just have the hot water on. Now when both the hw and htg are on together the boiler is fine. But when i turn the room stat down to zero the boiler gives me the noise problem. It happens when the boiler fires up (green light on), makes the vibrating noise then the light goes out. I've had the boiler serviced and setup to run correctly but the noise is still happening. I've been told its to do with the flow. It also has a bypass fitted in the airing cupboard and there is one 3 port valve. Any ideas on a solution?