It might be these new energy saving pumps. I’ve just put my boiler central heating temp up from 68 degrees to 71, forget condensing mode. A few years back on an energy efficiency course, we were advised to set the boiler to max and control the room temperature with the trv’s and room thermostat. Put it on max, it fires up once and gets up to temperature quick and then goes off makes sense. I’ll revert back to the old way and see if it makes any difference.