I been off grid 13 years in the UK.
Re combi boiler not igniting on a pure sign wave generator. I had the same problem at the start but solved it simply.
My pure sine wave inverter generator has two 13amp 3 pin normal, UK domestic plugs outputs (it's a 1.8kw suitcase module) plug the house in as normal. The other outlet I wired a plug with just an earth and a neutral NO LIVE!!!!
Then I stuck two earth rods in the ground 6 inches apart and connected the earth to one and the neutral to the other.
Dont ask me how or why this works but it does. My brother suggested it, he is an electronic engineer.
He said on grid live and neutral come together or wrap around each other in the power station and off grid this does not happen.
The first inverter I purchased 12 years ago setting always showed and earth fault and no tripping!! As soon as neutral was grounded all was resolved.
Now I have upgraded my system my knew Victron inverter takes care of this an so the neutral is no longer in the ground It will also trip a big diesel generator to charge the batteries when required. When this happens I can't run the boiler and so if I want hot water or central heating during this time, I will completely unplug the house from Victron and batteries and diesel generator and switch to the pure sine wave inverter geni 1.8kw with the earth and neutral in the ground.
So I have the house in no way connected to the national grid but have two armoured cables under ground into the house and one big plug from my so consumer unit so I can run the house from Either system.
Hope that all makes some sort of sense
