If your shower runs excessively hot and is difficult to regulate, the cause is usually a faulty thermostatic valve, incorrect boiler temperature setting, or restricted cold water supply rather than excessive mains pressure. Temperature imbalance often occurs when the mixing mechanism fails to blend water correctly. In most cases, the issue is local to the shower valve rather than the entire plumbing system.
The Most Common Reasons This Happens
1. Faulty Thermostatic Cartridge
The cartridge inside the shower valve may fail, allowing too much hot water through.
2. Boiler Temperature Set Too High
If the boiler output is set excessively high, the shower may feel overly hot.
If other taps are also very hot, see:
3. Cold Water Flow Restriction
If the cold supply is partially blocked, hot water dominates the mix.
If pressure also fluctuates, see:
→ Why Does My Shower Pressure Go Up and Down?
4. Internal Valve Wear
Over time, mixing valves lose precision, affecting temperature control.
Is This Serious?
It may be minor if:
- Only the shower is affected
- The issue started gradually
- Other fixtures work normally
It may require attention if:
- Temperature cannot be adjusted
- Water becomes dangerously hot
- Multiple fixtures are affected
What You Can Do
If your shower is too hot, you can:
- Check boiler temperature settings
- Adjust the shower control carefully
- Test cold flow separately
- Monitor other taps
If temperature remains uncontrollable, valve replacement may be required.
For related issues, see:
→ Shower Problems Explained
→ Why Is My Shower Not Getting Hot?
→ Plumbing Problems Explained