Sounds like it could be the DHW (domestic hot water) Thermistor.
It's just a little sensor that screws into the pipework and detects water temperature. If thats faulty it will cause the taps to run at luke warm temperature.
If your radiators are ok, then don't panic,...these are usually under £10 at any Parts Cenetr/Plumb Center.
Good luck.
Northern Knight
February 2010
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