With lever-style taps, why is cold water only added to the mix the further up the tap is pushed?

Question

I have several lever-style taps throughout my house - up/down controls the speed of the water flow, and left/right the temperature (left = hotter, right = colder). I have a hot water tank, and as a result these lever-style taps mix both hot and cold water - hot from my tank, and cold from the mains water supply.

When any of these taps are only slightly on (only lifted to the up position ever so slightly), I've noticed that the mix between hot/cold water isn't equal - only hot water flows from the tap, but the further up I push the tap the more cold enters the mix. This definitely isn't an issue with the tap; it happens to all of these lever-style taps throughout my property. Why can this behaviour be observed - is there any particular reason that these taps work in this way? Logically, my thinking would be that no matter how far up the tap is pushed, an equal amount of hot/cold water would be mixed together - but this doesn't appear to be the case!

Answer 1

It could be a pressure imbalance in the hot & cold lines, the valve cartridge being slightly off center, the design of the valve, or even thermal expansion or contraction within the valve. It's not uncommon for the hot/cold mix to be unbalanced at very low flow, just adjust the lever a little.

Answer 2

It may also be the hot water heater/source is set at a lower temperature.

Answer 3

You say:

This definitely isn't an issue with the tap; it happens to all of these lever-style taps throughout my property.

This does sound like it isn't a problem with a specific tap (e.g. the seals are worn, the shutoff valves aren't completely open, etc). However, this could easily be a design problem with these taps, such that all of the same make/model tap show this issue. You imply that the non-lever-style taps in your property do NOT have the problem, which would confirm this conclusion.