To adjust your thermostatic shower temperature, remove the temperature control cover, turn the spindle clockwise to make it colder or anticlockwise to make it hotter, then reassemble and test the temperature before tightening everything back in place.
If you’re still experiencing issues or need further clarification, we recommend watching our comprehensive video guide on how to adjust a thermostatic shower valve and resolve common temperature problem.
What Is a Thermostatic Shower Valve?
A thermostatic shower valve automatically mixes hot and cold water to deliver a stable, safe temperature. Unlike manual mixer valves, it adjusts instantly to fluctuations in water pressure, protecting you from sudden temperature spikes.
What Are the Common Problems with Thermostatic Shower Valves?
If your shower isn’t maintaining a comfortable temperature, it’s likely due to one of the following:
- Water too cold or too hot, regardless of dial setting
- Temperature fluctuates during use
- Dial won’t go past 38°C, even when more heat is available
- New boiler or water system changes have thrown off the valve balance
- Hard water limescale has affected performance
These issues usually stem from a misaligned or stuck thermostatic spindle — and you can fix this without replacing the whole valve.
What Tools Do You Need to Fix a Thermostatic Shower Valve?
- Flathead screwdriver or Allen key: To remove the control knob and access the spindle
- Thermometer (optional): For precise temperature measurement
- Clean cloth or towel: To protect surfaces and catch drips
- Descaler (optional): For cleaning a scaled-up thermostatic cartridge
How Do You Adjust a Thermostatic Shower Valve (Step-by-Step)?
Step 1: Turn Off the Shower
Before you begin, make sure the shower is fully switched off. You don’t need to isolate the entire water supply for this task, as you won’t be removing anything pressurised — just surface-level components. It’s also a good idea to let the area dry slightly to prevent slipping or dropping tools.
Step 2: Remove the Temperature Control Knob
The temperature knob is the dial that typically controls the heat level. To access the internal adjustment spindle:
- Look for a small plastic cap at the centre of the knob. This cap is usually hiding the fixing screw underneath.
- Gently pry the cap off using a flathead screwdriver or your fingernail.
- With the screw now visible, use your screwdriver or Allen key (depending on the screw type) to remove it.
- Carefully pull the knob off to reveal the spindle or cartridge stem underneath. If it feels stuck, wiggle it gently—do not force it.
Step 3: Locate and Adjust the Spindle
With the temperature knob removed, you should now see the adjustment spindle, the small metal or plastic shaft that controls water mixing inside the valve.
- To make the shower colder, turn the spindle clockwise.
- To make it hotter, turn it anticlockwise.
Make very small turns, about a quarter rotation at a time. After each adjustment, loosely place the knob back on, run the shower, and check the temperature.
Tip: Use a thermometer to get an accurate reading. Aim for 38°C for standard use, or slightly higher if desired—but never above 46°C for safety.
Step 4: Reposition the Safety Stop (if needed)
Some thermostatic valves have a built-in safety stop ring that physically limits the dial from going past 38°C. If your shower won’t go hotter, this ring may need to be removed or repositioned.
- Gently slide the ring off or rotate it further to allow the knob to turn more.
- Once repositioned, reinsert it so it stops the knob at your new preferred max temperature.
Always ensure that the final setting is safe—especially in homes with children or elderly users.
Step 5: Reassemble the Control Knob
Once you’re satisfied with the new temperature setting:
- Place the knob back over the spindle.
- Reinsert and tighten the fixing screw securely.
- Press the plastic cap back into place to cover the screw.
- Wipe the area with a clean cloth to remove any water or fingerprints.
Step 6: Test the Shower Thoroughly
Turn the shower back on and let the water run for 1–2 minutes. You want to confirm that:
- The temperature is stable (no sudden spikes or drops)
- It reaches the desired warmth within 30 seconds
- The control dial now reflects your preferred heat range
If it feels right congratulations, your valve is now properly adjusted!
What If the Adjustment Doesn’t Work?
If you’ve followed the steps and the water temperature still won’t change or fluctuates unpredictably, your thermostatic cartridge may be blocked with limescale or worn out.
In that case, you’ll need to:
- Remove the cartridge (this may require water supply isolation)
- Soak it in a descaling solution or white vinegar
- Replace it if cleaning doesn’t restore its performance
Replacement cartridges are available online or at plumbing stores. Be sure to match the part with your specific valve model.
When to Call a Professional Plumber
While adjusting the temperature spindle is safe for most DIYers, some situations are better handled by a qualified plumber. If your valve is concealed behind a wall or tile, or if you notice leaking, cracking, or unusual resistance when turning the dial, stop and call an expert. Similarly, if you’ve recently upgraded your boiler or water system and aren’t sure whether your valve is still compatible, professional advice can prevent bigger issues down the line.
Summing Up,
Fixing a thermostatic shower valve is often quick, simple, and well within reach for most DIYers. A small adjustment can make a big difference to your comfort. If things still aren’t working, don’t hesitate to call a plumber — a quick fix today can prevent bigger problems tomorrow. Keep your valve clean, your cartridge in good shape, and enjoy perfectly balanced showers every day.
