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Downstairs sink gets scalding hot. Bathroom sink (which is 2 ft from shower) gets scalding hot. Shower gets medium hot at best. Any non-plumber fixes here?

closed as off-topic by mmathis, Daniel Griscom, ThreePhaseEel, Tyson, Machavity Jan 25 '18 at 18:37

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    What kind of valves are on each fixture? Do any of them have temperature-regulating mixing valves? "Scalding hot" is bad anywhere but a commercial kitchen, however tanked water heaters must now be kept at scalding to stop legionella. (Legionella is not new, what's new is that we understand its mechanism now.). This requirement thus necessitates anti-scald mixing valves everywhere, – Harper Jan 23 '18 at 0:25
  • Hello, and welcome to Stack Exchange. As @Harper noted, we'll need more info to help you. – Daniel Griscom Jan 23 '18 at 2:22
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    @Harper I thought that thermostatic mixing valves were only required and installed on showers and tub/showers. I thought that the kitchen faucet and even the bathroom lavatories were allowed by code to deliver very hot water. Am I wrong? – Jim Stewart Jan 23 '18 at 4:16
  • You can buy kitchen faucets with a mixing valve built-in but I don't think they are required by code. Ditto, bathroom sink faucets. – ArchonOSX Jan 23 '18 at 17:13
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It sounds like the shower has a thermostatic mixing valve. These do have an adjustment to change the temperature limit if you want hotter water. I must say however that showering with very hot water may feel great, but is not really good for the skin.

Research the matter, but I would say that the temperature of full hot from a shower should not be over 110 F, but evidently the code is 120 F maximum. https://www.phcppros.com/articles/1828-hot-water-system-temperatures-and-the-code

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Check your shower tap should be automatic: one side a knob wit degrees on (and a button to press for turning hot water knob hotter than 38°C) and another knob to adjust the water flow intensity.

If you have only a single lever, your mixer may be blocked by limestone and has to be replaced

  • I don't think the OP lives where you do. Most faucets in the US don't have temperature adjustment knobs. – ArchonOSX Jan 23 '18 at 17:15
  • US US US... just 4% of people live in the US. So it's by-far more probable that he doesn't. – DDS Jan 24 '18 at 18:30
  • Okay, but percentage wise more people that post here are from the USA. – ArchonOSX Jan 24 '18 at 20:20
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Hit the cold water shutoff just before the offending shower, then set the water as hot as you can. You should get much hotter water. That means that you either have a thermostatic/anti-scald mixing valve or the fixture itself limits how hot you can set the water. Either way, it should be adjustable or you can swap the fixture out (although swapping fixtures may fall into plumber territory).

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