Before I suggest what might be causing your problem � the following is a pr�cis of what happens when your boiler should fire up.
Once either a demand for central heating or hot water is made on the boiler, the boiler switches on the fan (to the combustion chamber). The combustion chamber can be considered as box containing the gas burner & heat exchanger. To operate correctly, the fan must be drawing air through the combustion chamber and expelling the exhaust fumes (via the flue ducting) out of the house. To ensure this is happening, the boiler is fitted with a pressure switch, which is monitoring the pressure differential between pressure within the combustion chamber and that within the exhaust flue.
The boiler will only ignite if this switch detects the minimum required pressure differential. If the required pressure differential is not achieved within a specified time, or drops below the minimum level for some reason, the boiler will shut down and require re-initialisation. This is an important safety feature of the boiler, otherwise poisonous fumes can be given off by the boiler.
Based on the above working of a combi-boiler, your problem may be caused by a number of things:-
If it really is strong winds causing the problem, it might be that your fan is on its way out.
Other possibilities include the tubes connecting the pressure switch being perished (leaking), giving a false pressure reading, or the pressure switch itself being faulty, a further possibility is that the (cover) seal on the combustion chamber is leaking.
Bear in mind that combi-boilers are complex things � you may have some other fault, leading you to believe that strong winds are blowing the flame out � this should never happen with the fan being powerful enough to counter any external pressure changes (due to the wind).