On 14/01/2016 17:58, Phil L wrote:
wrote:
Hot water getting red hot at sink next to boiler but only just above
cold up stairs any ideas

Run upstairs water 4 mins report back with temp


That's certainly the first thing to try. 4 minutes is probably a bit
cautious. Do you get the same flow rate upstairs as downstairs? If it is
much slower, then the combi may be cutting in and out.

Can you get water out of the upstairs tap when the downstairs one is
running? (You might have to reduce the flow of the downstairs one).
There will be some heat loss in the pipe run upstairs, but this should
not be particularly obvious unless it is a horribly long run, for some
reason. So with the combi running, and both taps running, you should get
similar temperatures at both points eventually. If you don't, this
suggests that as Andrew suggests, the plumbing is more complicated than
you think.