A manifesto on shower temperature control
Much of the confusion in this  thread comes down to the fact that in the US, the standard shower valve is a 'pressure-balanced' valve, which allows you to select a flow-ratio between hot and cold feeds, but does not in itself maintain any particular temperature - it just ensures that in the event of pressure changes on one or other feed, the overall mix is maintained (preventing temperature spikes if someone flushes a toilet).<p>Whereas in many other parts of the world, the standard shower valve is a 'thermostatic mixing valve', which allows you to select a temperature, and balances the inputs to  achieve that desired temperature mark.<p>Note that if you go to, say, HomeDepot.com, and look at shower faucets, you <i>will not find thermostatic mixing valves</i>. Only pressure balanced. The only thermostatic component in conventional american shower valves is an anti-scald-cutoff. Thermostatic valves do exist, but  they're not the ones that are bundled into showers and that  therefore get employed by the average landlord who is grabbing the  cheap standard parts off the  shelf. Thermostatic is a premium option, and not one that even crops up in the search result filters for showers.<p>So most Americans have simply no idea that thermostatic valves are a thing.<p>Whereas if you go to, say, diy.com (which is the store of B&Q, an equivalent store in the UK), and look up showers, you will find all the basic 'mixer showers' have thermostatic valves.