Campbell Scientific Hydro-Wiper-C Operation Manual from Zebra-Tech - Manual (Page 7)

Hydro-Wiper operation manual
Zebra-Tech Ltd 6
wipe. The diagnostic LED will flash twice every 15 seconds whilst
this situation continues.
Maintenance
The Hydro-Wiper requires very little maintenance, and should
provide reliable operation for many years.
The only user replaceable part, apart from the batteries, is the brush.
Under normal conditions, the brush should last many thousands of
wipes. If however the brush does need replacement, these can be
obtained from your supplier or directly from Zebra-Tech Ltd.