21-04-20, 10:06 AM
As others have said it is probably the hot water pre-heat system where the heat exchanger within the boiler is kept up to temperature so you get hot water at the tap quicker. My own boiler is a Worcester Bosch and you can turn Eco mode on which stops it doing that, which is what I have done.
The other time it might start on its own when the boiler is turned off is for frost protection below about 8 degrees, but obviously not in this case.
The other time it might start on its own when the boiler is turned off is for frost protection below about 8 degrees, but obviously not in this case.