Low Hot Water Pressure

[Mr-H]

A few months ago we had a new sink/mixer taps fitted to the kitchen. I have been unhappy with the speed of the hot water since then. I have been told by the company which fitted the sink that it's 'about right', but I don't think it is. There is a downstairs loo not 10 ft. from the kitchen tap - it takes just 4 seconds to fill a pint jug with hot water here, whilst in the kitchen it takes nearly 15 seconds for a pint (imagine how long it takes to fill a washing-up basin!!). I have heard that some mixer taps can suffer from some form of twist in the pipe during installation(?), but wonder if this current pressure is acceptable (I don't think so), or whether/where I should perhaps look for a kinked pipe? Any suggestions gratefully accepted please.

[The Builder]

I'm afraid this is quite common Mr H. In your loo, you probably have an older type of tap. One that allows water to flow "straight through" with no restriction.

Modern kitchen mixers often have only 10mm tails to connect to the H&C supplies. Older taps are 15mm.
That's fine with the cold at mains pressure, but your hot sounds like it's gravity fed from a roof tank. The flow volume gets restricted.

Also, it's common practice to put isolating valves on the supply pipework. These valves choke the flow down to around 6 or 8mm. That makes it even worse.

Mixers are fine with a Combi boiler since the HW is at mains pressure (same as the cold).

You could fit a pump under the sink, but it does add to the cost. You could also look for a kink in the hot tail. Probably a metal braided type (a bit like chainmail!) I'm inclined to think it's simply a case of restricted flow though.

[Mr-H]

Many thanks, builder. What can I say - b**ger!!

[Mr-H]

I am of a mind to switch the tails over, making hot water come out of the mixer tap where the cold should and vice versa to see if my problem is solved. It has, though, been suggested that this may not be permitted - is this correct? If so, why?