Can I ask how you fill the boiler? Do you just pump from the tender or direct to boiler? Only reason I a#k is I’ve just finished mine and thinking of best way. 👌
Before firing I fill it via the removable plug on the cylinder block. I don't know if yours has one but normally they do. Then whilst under steam I use the crank-driven-water-pump which draws water from the bunker tank and tops up the boiler against pressure as required. I'm not sure yet but the injector on my machine may need some attention as it's not too happy. Injectors can be problematic generally.
