The device, which was adorned with wires and red flashing lights, was on the kitchen table courtesy of an unhappy tenant who had earlier refused the workmen entry to his flat.
A Royal Navy bomb squad was dispatched to deal with the package. Upon inspection they revealed it was an elaborate hoax designed to scare away the unwanted visitors.
A source said: 'The two men got the fright of their lives - the package looked real enough to the untrained eye and they must have thought they were done for.'
The man had stopped South Lanarkshire Council carrying out the free, routine tests on the boiler at least three times before this incident and he insisted the hoax was a joke.
He said: 'It was just a carry-on at work. Nothing more than that.'