If the boiler is starting up, getting hot, and shutting off before the house gets warm, one likely cause would be something is stopping the hot boiler water from getting to the radiators.

It could be as simple as an air lock. Or, a bad pump somewhere. Or, bad controller for that pump.

If that were the case, I would expect the thermostat to keep calling for heat, and the boiler to be maintaining its setpoint, whatever that is, and coming on and off just enough to keep the boiler water from getting cold.