DHW on my Baxi 105e?

I have a problem with my hw on my 105e ,to start with for some time the hot water would not fire up the boiler and I had to run the bath tap for it to fire up , now the same thing is happening but the hot water only gets to 50' and wont get any warmer. I also noticed that if i turn on the pre heat it takes ages for the tempreture to come up.
P.S. When I did get it to work with running the bath I had to turn the tap back to get the bath realy warm