Police are appealing to anyone who saw a man on Westergate Street in Chichester around midday on Friday (November 23).
At 12.15pm the man called at a house of a woman in her 90s and told her he needed to check her radiators.
He waved a clipboard at her before walking into the house.
He looked at the radiator in the lounge and then went upstairs.
The victim told him her daughter would be round any minute and he left immediately.
Some of the drawers and the jewellery box in her bedroom had been opened but nothing had been taken.
The suspect is described as white, between 23 and 25, slight build, no facial hair, medium length mousey brown hair, 5ft 8in and spoke with a local accent.
He was wearing dark coloured clothing, dark coloured jacket undone with a grey pullover underneath with a dark possibly criss cross pattern.
A Sussex Police spokesman said: “Always use a chain on your door if you are answering to someone you don’t know and don’t be afraid to ask to see some ID which you can look at properly. If you are in doubt, don’t let them in and phone the company they claim to be from using a phone number from a telephone directory. If you are suspicious then call police on 101.”
Anyone with information about this incident is asked to call police on 101 quoting serial 0669 of 23/11 or the independent charity Crimestoppers anonymously on 0800 555 111.