Thank you for your enquiry.
Regarding the Earth Relay Fault on the PT300:
Try switching off your instrument and then switching on again with no leads attached to see if this clears the error.
However if this persists / will not clear, your instrument needs to be returned for inspection / repair. For further information / help with your unit please contact:
Unit 11 Bracken Hill,
South West Ind. Estate,
SR8 2LS, England
TEL: +44 (0) 191 587 8739