Boiler gas to water heat exchange is making clicking and kettleing noises. All radiators have been bled and boiler / pump have been bled too, so there is no air in system. Boiler starts to make the noises when the gas is at maximum velocity. Pump is running on top speed, when pump is turned down this does reduce the noise, but manual says on a combination boiler keep the pump running at maximum speed.
Any ideas would be a great help.
Any ideas would be a great help.