Jellis

Can you try it this way ? What I'm suggesting is to clear the mismatch, enable the mismatch interrupt and then sleep

Code:
    IOCA = %00001000    ' Enable RA3 as on-change-INT ***this could be made permanent before main***
    ' clear the mismatch condition
    dummy = flush
    INTCON = %10001000  ' Enable interrupts: global & RABIE, but TMR0 disabled ** and RABIF is cleared **
    @ sleep
    ' Microcontroller is in Sleep State waiting for external FLUSH Interrupt
        ' Valve should be closed at this point and no water flowing
   GOTO Main    ' Loop to Main to wait for next Flush interrupt on RA3 change