Water has started pouring out of the overflow pipe in the shower unit as well as the normal shower outlet when switched on. Any ideas as to what the problem might be?
Same happened to me yesterday. My research suggests that "the PDR has popped". Essentially, a pressure release valve has yielded, possibly because the shower head was clogged. giving you a bill for £7.95 or thereabouts, and a bit of DIY. At least, that's the action I am taking.
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Try fixfault.com to fix plumbing.