I think wood is only carbon neutral if it is being burnt at a rate no faster than it is being supplied by new growth. Historical deforestation shows that this generally does not happen. Probably the only way to live sustainably is to liquidate a significant part of the world's population, or alternatively the whole of the North American population and their associated flatulent cows and fields full of car fuel.
The eco-warriors will get round to suggesting this soon. They would do anything rather than go back to nuclear power.
Feel free to flame me if you think the atmosphere can take it
On gas boilers, I am pretty sure the thermistor is just a pressure device. It is the main gas valve that needs electricity to hold it open - this is low voltage, 12 or 24v, can't remember which. A battery will do it. Unless you've got a gravity circulation you'll need power for a pump, too. They are 220v in my experience, so that's the bigger problem.