hot water turns tepid in minutes,c/h ok

[dickythemint]

HELP !!!

I have a Range Powermax 155 boiler around 5 years old

Just lately when the hot tap is turned on i only get a few litres of hot water then it turns tepid. If i turn the tap off for a few minutes and back on i get the same again.
The central heating is working fine and the boiler seems to fire ok on heat demand.
I had new kitchen sink few months ago and turned off water stop tap for couple of hours , other than that the plumbing has not been touched.

Has anyone had this problem or does anyone know what the problem is please

 

[baxpoti]

Exact model of 155 ?

Problem is most likely to be the hot water pump or blender

 

[dickythemint]

from what i can gather its an OV 155.

the pipe above blending valve is red hot and the pipe below is cold and the pipe to rh side goes cool when hw is run from taps.
i have turned temp up on blending valve and the same happens but obviously the water is at higher temps (scalding down to warm)