D600 Unable to reset UCCNC. Testing limit switches.

Everything working OK. Total runtime of m/c since construction is about 12 hours on various projects. Turned off overnight. Switch back on following morning and unable to clear reset in UCCNC. All limit switches move and click when manually poked but the diagnostics don't change. It looks like either the X or Z limit switches has failed.

Before I dismantle to gantry to access the actual microswitches are there any suggestions for other things to try?