I am a UK homeowner with a residence we describe as "new build" (made in the last 8 years, timber frame etc).

The boiler is on the ground floor in the kitchen. It is gas heated from the main gas line supplied to the house. On the first floor I have a shower which is plumbed directly into the bath taps.

The water from the bath tap is exceptionally hot and to run a bath can be scalding and require cold water...but the shower (rainfall showerhead) starts hot but then retreats to being merely warm at it's highest setting. Warm is the highest temperature it can muster.

What causes this and can it be fixed?

  • Could have a thermostatic or pressure balancing regulator. I don't know this with any certainty, but the hot start may be a transient until the regulation settles on its setpoint.
    – Hari
    Feb 28, 2017 at 23:35
  • When you say you have a 'boiler' exactly what do you mean? Is this only a water heater for the potable hot water for kitchen, lavatories, showers, etc., or does it also supply hot water for space heating of the house? Feb 28, 2017 at 23:48
  • The house is heated by central heating radiators in each room. The boiler supplies hot water to the taps and shower / bathrooms. Mar 1, 2017 at 0:04
  • So the boiler supplies heat (as hot water) to the 'central heating radiators' and to the potable hot water outlets? In this type of system (I think called a combination boiler in the US) how is the potable water separated from the water that goes to the radiators? Mar 1, 2017 at 13:28

1 Answer 1


You have a regulator in the faucet or shower head that keeps the water below scalding for safety purposes. You can adjust it by either removing the faucet knob adjusting the safety feature or removing the shower head and adjusting it's safety feature.

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