greenstar 28i - warm not hot water

[helly]

sorry if this is similar to an earlier post! our 9mth wb greenstar 28i has worked perfectly since installation until it a few days ago when the water went warm/lukewarm. We had a new bathroom fitted before xmas with mono basin, mixer bath taps (so think ceramic disc),but the water was fine with these. Have reduced the flow rate at the tap but it didnt make a difference but the water is hot when run very first thing in the morning but then cools again. CH is working fine.

Can anyone offer any advice as i have WB coming out on friday and i am kakking it incase it isnt a boiler fault and get stung with a hefty call out charge.

many thanks

 

[helly]

sorted apparently not enough gas getting to the burner and a new diverter motor, lots of toasty hot water