More than 70 blankets were checked last week by Rhondda Cynon Taf officers. Sixty-seven per cent failed and more than half had serious faults.
Electric blankets account for 5,000 fires a year in the home and the over-60s in RCT were encouraged to get theirs checked out.
Thirty-eight were condemned as unsafe and were immediately replaced.
Ten blankets were failed due to unsafe plugs and the defects were put right by the test engineer.
Twenty-six double and 12 single blankets were replaced.
Councillor John David, cabinet member for health and adult services, said the results were horrendous.
'Many of these checks have been vital in saving lives, that is why they are so important,' he said.