The small nut and bolt which protrudes between the element ends should be loosened but not taken off,you now press inwards on the bolt, this will relax the compression on the rubber sealing block, this should allow you now to extract the old element..
make you fit the new one in correctly as the drum will not turn, put a smear of silicon seal around the rubber do not over tighten the heater nut, test for a leak with a kettle of water
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