We have two level transmitters for FCC reactor. Since last few months back we are facing malfunction of one of the level transmitter. We use to flush/ blast the High pressure tapping of that level transmitter for few minutes. The transmitter works well again for few days after flushing. We observed that there is no any effect to the other transmitter. The Low pressure tapping of both transmitters are at same elevation and High pressure tapping are at different. What could be the possible reason for this case? Or it was only due to bubbling bed fluidization issue or due to damaged/ plugged air grid.