LNB is low noise block. It's the bit in the middle (most often coloured blue
Now that is obscure, LNB's are not usually blue, that I can tell you for sure - what colours? Cream or Black probably.....
The satellite Dish is under a two year warranty
I'm sure it is, but if the dish has been knocked in the wind or water got in somewhere in a storm over the winter, that may not be regarded as a fault as it is not broken. It does sound like your dish may have been knocked or moved in the wind, so could be in need of a retune - unless you have a faulty LNB. The signal is a little weaker in the morning, then gets stronger & then can weaken in the evening.
It is all channels or just the ones you are watching, have you checked all? For example you are unlikely to get ITV HD as signal too weak, even if dish tuned - so no fault. Are you using a ky box, which restricts which content you can see as is regionalised & some weaker than others - so can be a Sky box problem (if you have a Sky box).
Could be a few things, though given the levels of storms we saw over the winter, it may simply be a case if dish not been looked at for a while, may need a tune.