I have just had a new wet room fitted and since I get hot water sometimes and sometimes not!
I have a combi boiler. The problem is the same throughout all the taps in the house. The shower seems to be ok but it can run cold for a few seconds when showering.
When you don't get any hot water is the central heating on? Sometimes there is a valve in the boiler called a diverter valve which sends the hot water to the taps.
Have you tried resetting the boiler, what make is it and how old?
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