Please can someone advise me. I have a newish built home 6 years old which came with a new baxi combi boiler which has never given me any problems. Then four days ago I realised the taps in the bathroom (both sink and bath) are only giving out luke warm water. The shower is still fine and not connected to the taps. The taps aren't mixer taps either. I've tried turning the taps so water slowly comes out and the water gets a little hotter but not enough and by the time the bath is full its cold! Please help as I don't know if I need a plumber or if it's the boiler although the kitchen and downstairs toilet tap are both fine. Thank you

It sounds a lot like you have one bad element. The only way to know is to turn off the power and remove one wire from each element and test each one with an ohm meter. Check across the terminals and then to ground (the metal parts on boiler are grounded). Any reading to ground means that the element is bad, and it is dangerous, too. When reading across divide ohms into voltage to get amperage and if it does not match what it is supposed to be replace that element. You should also check the thermostats and see if one is staying open. Here is a booklet: https://dl.dropboxusercontent.com/u/8010163/How%20to%20use%20Test%20Equipment%20Service%20Manu al.pdf
https://dl.dropboxusercontent.com/u/8010163/How%20to%20Diagnose%20and%20Fix%20Everything%20Ele ctronic.pdf
Some boilers also have holding relays that if bad will give the same symptoms. You could have an open coil on a holding relay which would cause it to turn off the elements before the water is hot enough because one thermostat turns boiler elements on, then holding relay is energized and keeps boiler (even though first t-stat opens) on until second thermostat breaks the connection to coil on the relay, otherwise it will turn off when first t-stat opens instead of waiting on breaking t-stat to drop out holding relay. That is what separates boilers from regular hot water heaters.