'Thanks' for the no responses
but never mind, I got it worked out. The active fireman is actually taking care of the filling of the boiler, that's for sure. I still don't know exactly why the K4 was running out of water on several occasions but I have been driving a few scenarios again paying more attention to the boilerpressure and steam usage and the boiler filled up OK and in a timely matter. I think there may have been a problem that there was not enoigh steam left for the injectors to fill the boiler, especially when going up-hill. Having solved the problem I can really recommend the K4; really fun to drive. Sounds and steam effects are very nicely done. Nice extra is also the 2nd loco 'answering' the 1st (pilot) loco's whistle when double heading.
Leaves only the problem that in some cases (not always) the smoke and exhaust is blown violently to the side. Does anybody know how to remedy this?