We have had to rotate between an 8810 and 8810C in a system. Both units initially showed no signs of issues, however, both seem to intermittently cycle off after burning for an hour or less. They receive conditioned power from an ETA PD11SS. We have even bypassed the ETA and gone direct to the wall. Same issue. Both units have the latest firmware and will power again after a "hard" reset. Any logical advice. Thanks.