with such a low signal on 11 ( a stronger transponder???) and higher on others, i wonder if shoody cabling (old rg 59 cable) or bad connectors, or a splitter is the culprit?
did the installer use new cable , from the dish to your box?
what is the dish mounted to?
is there a tree in its line of sight?
during spring, when the leaves fill out the tree, this causes alot of dishes to lose signal if installed too low, or into the tree in the winter, while the leaves were gone, maybe if your lucky, the dish was installed less than 3 months ago....