Although the cistern empties (standard low-level) on occasions is does not flush away waste matter properly. Even just a couple of sheets of paper are sometimes not flushed away. The cistern empties completely (but does take a while to refill) & there appears to be no blockage in the toilet pan/waste pipe; the water level in the pan is always the same & always goes back to the 'normal' level on flushing. Any ideas please? The cistern was renewed about 10 years ago.