DIY wrote:

am I right in thinking that a
850watt 2 stroke generator would be powerful enough to power the condensing
combo boiler to give us hot water (maximum power consumption 140watt) and
maybe some small electrical appliances all well under 1kw?

All at once? Possibly not, depending on what you mean by "well under
1kW". I'd say 500W is "well under 1kW", wouldn't you? But that generator
won't power 2x500W.

The other thing you need to know is that the generator isn't 850 watt.
It may be plated at 850VA which isn't quite the same thing. And that
rating will be a maximum and the generator will probably be closer to a
450VA generator. If it's one of the two stroke generators with an
auxilliary 12V output then it doesn't really matter what it's badged as
or what the claim is for output, it wil be a 450VA generator. I've got
one (badged Cosmo, identical to the Wolf/NuTool/Pro User/Munro etc.) and
it's OK for running a drill, powering a few lights in a barn, recharging
a tractor battery, operating a TV, and charging a laptop while running a
printer. It could certainly power a water pump/boiler for a time.

Just don't expect to power multiple items simultaneously, it won't do
it. That 850W figure indicates that it can handle a transient switch on
load of 3.5 Amps. Try to maintain that continuously and you would damage
the generator. I've seen them with burnt-out windings, melted insulation
and damaged sockets from trying to run at 3A continuously. If you try to
run a load of 2A you will hear the engine labouring.

If you want a cheap stop gap, they are usable. Two strokes are also
ideal for standby use since they are robust, almost maintenance free and
you can put it in a garage for years on end and as long as you keep it
dry it will run fine when you fill and prime it.

If you do store it remember to drain the carburettor, because if the
fuel evaporates the carburettor will be fouled by the two stroke oil
residue and then it will be a bugger to get started next time around.