Your sentence is understandable, but I would say... "Tomas! Don't use this shower, it doesn't work." It "hasn't worked" means that it has not worked in the past, but it doesn't mean it is not working now (in the present). If I paraphrased your sentence it would read like this..."Tomas! Do not use this shower, it hasn't worked in the past and I don't know if it's working now."