If it's a heat orientated lockout I would be looking at flow rate threw the tap, time the tap is left on and temperture of flow on the main heat exchanger which would help indicate movement issues between main and plate heat exchanger, defective thirmister, slow flow rate and long demand time can take a boiler out with latent heat.
If it's a ignition lock out I would be looking at checking boiler settings as per manufactures instructions, monitering working pressure.
Usually the only difference with the boiler in combi mode is it runs at maximum demand for longer than in heating, so it can suck a supply dry if the regulator is defective(rare), show up flue faults(rare) or the boiler can modulate down to a low setting and stay there longer than its designed to if the heat isn't being absorbed correctly by the plate heat exchanger.
Either way you should be getting more love from Biasi, we can all talk a good game but you have to be able to prove your points.