It might be less efficient, or it might not, and I don't want to put as much thought into it as ericmark has! I was querying you (apparently) saying the load had to be kept above 7kW as that was the minimum boiler turndown.
But I'm sure the difference in efficiency (whichever way it goes) between a boiler which turns down to say 25%, and one which goes to 15% is negligible.
