My unidare stopped working recently and it turned out to be a broken element. Although unidare/dimplex don't do spares for such an old model (WF18), there is a company in Clitheroe (www.storageheater.co.uk) that stocks or makes spares to order. With the new element it's now working fine again.
You might have difficulty finding an electrician willing to repair it (rather than sell you a new one), but it's feasible as a DIY repair if you have basic electrical knowledge and take sensible precautions. A cheap maplin multimeter and one-of-those-screwdrivers-with-the-neon-fuse-for-checking-live-voltage and would enable you to diagnose where the fault lies.
chris parkin, March 2007