Other switches work fine but when I switch to fx loop my pedals and the amp keeps cutting out. It's definitely not the pedals that are the problem but the fx loop part of my amp. It cuts in and out and the pedals won't work.

Anyone know what the problem might be? I am taking it to an amp repairer tomorrow but thought I would ask here first.
I always start simple.

First check your footswitch cable for any damage or looseness at the ends.

Then spray some electrical contact cleaner (like DeOxit) into the Footswitch.

Not 100% on that amp but Peavey uses a tube to control the loop on some of their amps. Try a new/good 12AX7 tube through all of the positions or if you know which one drives the loop.
Jackson Kelly KE3 - MIJ (Distortion/Jazz)
Jackson DKMGT Dinky (EMG 81/85)
ESP E-II Eclipse Custom (JB/'59)
ESP LTD EC-1001FR (EMG 81/60)
Fender MIM Strat

Mesa/Boogie Dual Rectifier Roadster 212
Laney IronHeart IRT-Studio
Peavey Vypyr 30
Peavey ReValver Amp Sims
TOOOO many T.C. Electronic Pedals. . .
All good people. It was the easiest of fixes. My pedal battery was flat. Can't believe I didn't think of that. IDIOT!