Baxi Combi instant 105HE problem

[tedley]

Hi, I have a hot water problem which i cannot figure out. When there is a demand for hot water everything appears to work fine, but after a couple of minutes the water goes from very hot to just warm. If I switch tap off for a short time and back on again, there is hot water and the process starts all over again. Any advice will be sincerely appreciated.
Thanks in advance

 

[45yearsagasman]

Plate heat exchanger is probably blocked.Can be cleaned(not always successful)or replaced and more than likely will be system contamination thats causing the problem in the 1st place.