Yes as the cistern is warning you...obviously. Your problem is with the float
valve inside cistern...washer has probably gone ...cheap and easy to install
otherwise you can replace the whole float-valve unit for around £12. You should
have isolating valve on the cold feed pipe to the cister if so isolate supply
to cister and drain by flushing. Simply dis-mantle by turning nut usually
plastic. Once loose will be able to dis-mantle float-valve.Simply replace
washer and put back into place and turn supply back on...