Enough power, yes. I would definitely fit a changeover switch though. Simple, cheap switch....... over to one side would be mains...... to the other side would be generator.
If you don't, and both supplies are connected (even in a power cut), your generator power would flow backwards through the consumer unit to the rest of the house.
I don't know this for sure, but another concern is the circuitboard in the boiler. It might not take kindly to spikes in the supply or fluctuations from a dodgy generator.