With my Baxi 105e instant, the hot water flow has to be very high before the boiler kicks in.

kevin, September 2008

Possible that the small water flow diaphragm has split or deteriated.

Ian, September 2008

Boiler has a flow switch to detect water flow when tap is open, tap needs to be open alot to make switch otherwise not enough water passing through biler will cause it to over heat and shut down then come back on again (cycle) if tap is fully open and water flow is good and boiler still fails to light, flow switch mayb block or stuck

baximan, September 2008