Water from bathroom basin taps flow changes

Question

Please firstly excuse my stupidity if this is a simple matter..... But I wonder if someone could tell me why the flow of the hot water reduces when I turn on the cold tap (they are separate, although the same happens with the kitchen mixer tap)? Might this be due to the configuration of the pipes.... I thought that the sources were different, with the hot needing to go through the (combi) boiler, but the cold not having anything to do with that.... Of course, I know nothing much (at all) about these things :o/

Also, there is some kind of nasty black build up inside of the taps themselves, which I attempt to remove but gradually builds up again. This is 2006-built rented property of rather dubious construction in some aspects, so I suspect that a half-hearted job has been done overall..... The landlord is not any help and I am not a DIY-er where plumbing is concerned. I purchased new taps but he will not fit them and besides, I do wonder if the problem is somewhere in the piping....? The water from the supplier is not contaminated.

I hope someone can help or advise me; I have brushed teeth with bottled water for two years now :o( Best wishes.

Answer 1

Since the hot water's flow rate depends on keeping the boiler pressurized, and this can only happen by feeding cold water to the boiler as you draw hot water, the total flow rate is limited by the flow rate of the cold water feed to the house. You will see a similar reduction in flow rate if you open both the bathtub and the bathroom sink's hot (or cold) faucets, or any combination of separate water valves in the house.