Hoping to get some guidance on what the source of my issue might be: I have a single handle bathroom sink faucet which provides very hot water when the handle is set for "warm" water. I tried reducing the incoming hot water by closing the shut off valve about halfway. Now when I try for warm water I get:

  • cool water when the handle is set to full open
  • cool to warm when the handle is opened half way
  • burning hot when the handle is opened slightly

I have already changed the cartridge in the faucet. Might the incoming hot water line pressure be too high? If yes, is there a way to reduce it?

  • Is this a new problem? Does any other faucet have the problem? Are both valves open below the sink?
    – isherwood
    Commented Feb 9, 2022 at 21:28
  • Not a new problem, but we now have children that use the faucet so we are trying to find a fix. No other faucets have the problem. Currently the cold line is fully open, the hot is about halfway open. Commented Feb 9, 2022 at 22:41
  • 1
    It sounds like the hot and cold supply lines are switched under the sink.
    – gnicko
    Commented Feb 10, 2022 at 2:38
  • Since this is a long-term issue, it sounds like the water heater temperature is set too high.
    – FreeMan
    Commented Feb 10, 2022 at 15:18

1 Answer 1


The shutoff valve (or, indeed, water pressure in general) is not a good way to control the hot water temperature.

You either need a faucet with a built-in and correctly functioning (and correctly adjusted, if adjustable) tempering valve (sometimes referred to as an "anti-scald" valve), or you need a tempering valve on the hot supply to the faucet.

The vast majority of faucets produced in the past 40 or so years have an anti-scald feature built-in, as many countries require that feature in their adopted plumbing code.

One approach is to put a tempering valve for the whole house on the outlet of the water heater.

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