Help with boiler fault on dhw

[cowboyplumber]

I'm pretty good at installing but pretty ****e at fault finding...
Mate in pub last night asked; dhw flutuates between hot and cold, but water at kitchen sink remains constant.
Boiler is a poorly insatalled vokera.
The other thing is he is on a shared main and the problem ocured when his neighbour went away over xmas, now he's back it seems to work ok .
Can anyone offer any clues.
Thanks,
cowboy

 

[cowboyplumber]

bump

 

[EliteHeat]

How is that possible? if hot water comes out of a normal outlet at x degrees at n litres / minute, then it will come out of other normal outlets at x degrees at the same flow rate minus perhaps a bit for long runs. But it won't fluctuate if the other tap doesn't fluctuate.

P.S. By normal I mean ignoring any faulty thermostatic or mixer taps which could confuse the situation.

 

[frankthegasman]

sound to me that the domestic hot water heat exchanger is partially blocked ,it will require exchanging if it is.and possibly the sytem may require a flush if it is blocked goodluck

 

[cowboyplumber]

Thanks guys. The blocked HEX sounds pretty likely - as I said it was shyte install. Proper stick a boiler in (ignore regs), stick a kitchen in, lick of paint and then move to France job ...