The feed for the pressure guage tees off the line that goes to the backflush solenoid. If you are a tinkerer type and confident taking things apart, you could remove the copper tube feeding the guage and see if its blocked. Obviously you dont want to do this if its still under warranty. If a bit of crud has gone into this tube, its unlikely to get washed out again as its a dead end to the guage, so doesnt get "flushed out" with water flow.
If its blocked by some dirt etc, would this be covered by warranty?
On my machine there was a blockage in the copper tube connecting to the brew head, which stopped the guage and backflushing from working. Once unblocked it all works fine.
The wire up the grouphead wont do much unless the blockage is close, there are too many bend to negotiate. The guage feed is a long way off.
There is heaps of info on this forum for taking the machine apart etc which was very useful.