Central heating combi boiler?

Hi, I have an old Myson Midas si combi boiler, it requires constant attention and still has a couple of faults. One odd thing I have noticed is that when the hot water is being used (eg a shower, bath etc) the boiler fires up and correctly heats the water, I have noticed though that periodically while the water is still running, the boiler will fire the ignition to re light the burner, is this normal (shouldnt it just lower the flame rahter than keep switching off the burner and re igniting)?
Thanks