I have two Grundig GUFSAT02SD boxes and a Humax Foxsat.
The Humax works perfectly but the Grundigs are terrible for losing channels. I can be watching say, CBS Reality then suddenly it will either splutter and flicker or go off completely saying channel not available. Mostly when one goes off I can still watch it on the other one. This is very infuriating and I have had the tech. come out three times now but he can't find the problem.
Any ideas ?

Welcome to the Forum!

A basic question to start with ... Do all the Grundigs have an individual direct connection to the dish ?

Yes, they are both separate connections. I bought a Goodmans box today and it works perfectly. I spoke to a fitter who told me the Grundig box is one of the worst out there and it is a very common fault to lose channels with them. Going to replace the other one tomorrow.