To adjust the hot water temperature in central heating, locate the thermostat or boiler control, then set the desired temperature, typically between 60-70°C (140-158°F).
Getting the right hot water temperature in your central heating system is crucial for comfort, safety, and energy efficiency. Whether you have a combi boiler, conventional system, or heat-only boiler, this guide will help you optimize your settings.
Checking Your Current Water Temperature
Before making adjustments, measure your current hot water temperature accurately:
- Run hot water for 20 seconds to ensure it’s at maximum temperature
- Fill a heat-resistant container (like a glass measuring cup)
- Use a cooking or baby bottle thermometer to check the temperature
Ideal Temperature Ranges
| Application | Recommended Temperature |
|---|---|
| General domestic use | 120-140°F (49-60°C) |
| Anti-legionella setting | 140°F (60°C) minimum weekly |
| Boiler operating temperature | 160-180°F (71-82°C) |
Adjusting Different Boiler Types
Combi Boiler Adjustment
Combi boilers typically have separate controls for:
- Tap water temperature
- Radiator water temperature
- Pre-heat temperature (circulating water)
To adjust a combi boiler:
- Locate the tap water temperature control (digital or dial)
- Make small adjustments (5°F/3°C at a time)
- Test results immediately at a tap
- Repeat until desired temperature is reached
For optimal efficiency, consider installing a quality thermostat control if your boiler doesn’t have precise settings.
System/Conventional Boiler Adjustment
These systems require adjusting the cylinder thermostat:
- Locate the thermostat (often on the hot water cylinder)
- Adjust using the dial or screwdriver slot
- Wait several hours for temperature changes to take effect
- Test with thermometer method
According to Ideal Heating, system boilers may take longer to respond to adjustments because the water needs time to cool in the insulated cylinder.
Immersion Heater Adjustment
If your system has immersion heaters:
- Remove the thermostat cover (usually requires a screwdriver)
- Adjust the thermostat setting
- Drain some hot water to test changes faster
- Wait for temperature to stabilize before final testing
Advanced Temperature Control
For more precise control and energy savings:
Outdoor Reset Controls
These systems automatically adjust boiler temperature based on outdoor conditions. As recommended by heating professionals, they can reduce boiler temperature during milder weather while maintaining comfort.
Smart Thermostat Integration
Some smart thermostats like certain Google Nest models can control both heating and hot water. These work best with:
- On/Off hot water tanks
- OpenTherm compatible systems
- Combi boilers with smart features
For homes with built-in gas heaters, smart controls can provide unified temperature management.
Safety Considerations
- Keep tap water below 120°F (49°C) to prevent scalding
- Maintain boiler temperature above 140°F (60°C) to prevent condensation damage
- Weekly anti-legionella cycles should heat water to at least 140°F (60°C)
- Never set boiler temperature above manufacturer recommendations
Energy Saving Tips
- Lower boiler temperature during mild weather
- Insulate hot water pipes and cylinders
- Consider a timer to reduce heating during unused periods
- Regularly maintain your system for optimal performance
