How do I change the maximum temperature on my shower?

Two different things get called the maximum temperature. One is the stop built into the valve, which is a physical limit set by a toothed collar and is adjustable. The other is the temperature of the hot water arriving, which is set at the cylinder or the boiler and is a different job entirely. If the shower will not get hot enough, it matters a great deal which of the two is limiting it.

Safety

What you'll need

• A bath thermometer, or a cooking thermometer that reads to 60°C
• A small flat screwdriver or an allen key for the handle grub screw
• Silicone grease

Step by step

1. Establish which limit you are actually hitting.Turn the temperature control fully towards hot with the override button pressed, run it, and measure the temperature at the outlet. If it reaches somewhere near the hot water temperature in the rest of the house, the valve's stop is what is limiting you and it is adjustable. If it stays lukewarm even at full hot with the override in, the hot water supply is the limit and the valve setting will not change it.
2. Find the override button.Almost every thermostatic valve has a small button, usually red, on the temperature handle. It is there so a user can pass the safe stop deliberately for a hotter shower. Pressing it and holding while you turn is the intended way to go beyond the stop, and for many households that is the whole answer — nothing needs adjusting.
3. Isolate the water before removing anything.Turn the shower off at its isolating valves or the stopcock. You are not opening the waterway, but a slip that dislodges a cartridge with pressure behind it is unpleasant.
4. Remove the temperature handle.Look for a small cap or plug hiding a grub screw or a retaining screw — often under the temperature indicator disc. Undo it and pull the handle straight off. Do not lever it, and note the position it was in as it comes off.
5. Identify the splined collar or stop ring.Underneath the handle is a toothed or splined collar. It has a lug or a notch that meets a fixed stop in the body, and that is what limits the rotation. Some designs instead use a separate ring with a screw. Photograph it before you move anything.
6. Move the stop one spline at a time.Lift the collar off its splines and refit it one tooth round in the direction you want, then refit the handle and test. One spline is typically a few degrees. Moving it several teeth at once and testing at the end is how people end up with a scalding shower and no idea what they changed.
7. Test with a thermometer at the outlet.Run the shower with the handle at the new maximum and put a thermometer in the stream at the head, not at the valve. Around 41°C is a comfortable and safe domestic maximum. Anything much above 43°C at the head is hotter than a shower needs to be and is into scald territory for someone who cannot get out of it quickly.
8. Set the marked temperature to match reality while you are there.The number printed on the handle should correspond to what comes out. If it does not, refit the handle a spline round so that 38 on the dial actually delivers about 38 at the head. A handle whose markings are wrong is worse than one with no markings.
9. Think about who else uses the shower.If there are children, elderly residents, or anyone with reduced sensation or mobility in the household, set the maximum lower rather than higher, and leave the override as the deliberate act it is meant to be. This is the one setting in a bathroom where the conservative choice is clearly right.
10. If the water is not hot enough at source, deal with that separately.A shower cannot deliver water hotter than the hot supply. If the cylinder or boiler is set low, that is where the change belongs — and it has its own trade-off between scald risk, legionella risk and standing heat loss.

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