Often I am asked by customers if we can install zones and thermostats on our high efficiency installations. When I begin to explain that we can not zone or install thermostats on high efficiency I am asked "how will i be able to control the system" and I answer "why do you want to control the system". There is no need to micromanage a high efficiency system, it is the perfect secretary... it knows exactly what you need and when you need it. However, if you feel that it's just too much letting go, you can install TRVs which control flow to each radiator individually and does not interfere with the boilers functions.
Why shouldn't you zone a high efficiency system?
Because a high efficiency system has to be on 24/7 and modulate to follow the load. The load is the key. A typical one family house barely has 100,000 BTU heat loss on a cold day let alone the average heating season day. A typical 100,000 BTU boiler (just as an example) can modulate from 20,000 BTU to 100,000 BTU before it shuts off because it doesn't see a load. If you zone the system you break up this load even further. The boiler will not see a load because it's under it's lowest modulation point (in non specific terms). This destroys all the comfort and efficiency of this wonderful system.
Why can't I have a thermostat?
Very simply, for a high efficiency system to be high efficient it must modulate and a thermostat prohibits it from modulating. To modulate means that the flame has to get higher and lower to keep the temperature at the right point to replace any lost heat from the building. If you install a thermostat you remove the boilers ability to modulate because you now control the boiler turning on and off. While this seems unfair to the feelings of the boiler since it knows best what it needs to do, it will also impact your comfort. These boilers do not have a high pick up rate like a standard efficiency boiler so it takes longer for the entire house to warm up vs a standard boiler. Each time the thermostat turns the system off it needs a significant amount of time to heat the building back up to a desired temperature. Aside from the fact that you are losing all your efficiency in that start up, you are also losing all your comfort because you are introducing temperature fluctuations which confuse your body.