Marco Arment commenting about the Nest thermostat:
The problem arises when the Nest needs to charge itself and neither the heat nor air conditioning has turned on in a while, like on a mild day. Without a C circuit to take power from, it can only charge itself from running the system.
So it pulses the R-W heat circuit in short bursts to get power.
Marco doesn’t think that is good for his boiler — and he is right because that’s not good. Best way to think of it: starting up your car and turning it back off, then repeating. Battery wear down on your car aside — cycling a heating system or your car’s engine that often is not optimal.
This isn’t likely something that will directly cause a problem, but it is putting unneeded wear and strain on your heating system — no way I would allow this.