This  paper  presents  results  from installations  comprising  both  HAE  and  LAE  filters  in  fully  grouted  boreholes  and  in  intimate contact  with  the  ground.  It  stands  out  distinctly  that  high  air-entry  filters  have  a  high  risk  of malfunctioning if placed in fully grouted boreholes with no possibility of flushing the filters. Low air-entry filters should be the preferred choice of filter for non-flushable diaphragm piezometers in fully grouted boreholes.