Trouble with hot water staying hot.

[BarbaraD]

Hello everyone i have a Halstead ace high combi boiler which is being a nuisance! When i run the hot tap it will stay hot for a while and then go cold and then hot again i am missing my radox soaks! Do you have any idea what this could be, and is it something i could tackle myself? If it's not too complicated that is.
Thankyou

 

[newbie1]

dhw plate heat exchanger scaled..not really a diy job

 

[BarbaraD]

Thanks, i'll have to find a man/woman who can sort it for me.