The EPH CP4M and EPH CP4B are both popular programmable room thermostats used to control a single heating zone. They offer similar functionality, including OpenTherm® compatibility and Boiler Plus compliance, but there is one key difference that often causes confusion when ordering.
The Main Difference: Power Supply
The only major difference between the CP4M and CP4B is how they are powered.
This difference affects installation and is the most common reason customers accidentally order the wrong model.
EPH CP4M – Mains Powered Thermostat
The CP4M is designed for installations where a permanent mains supply is available at the thermostat location.
Best suited for:
- New installations
- Replacements where a mains feed already exists
- Users who prefer not to rely on batteries
EPH CP4B – Battery Powered Thermostat
The CP4B runs entirely on batteries, making it ideal where no mains power is available.
Best suited for:
- Retrofit installations
- Locations without a mains supply
- Faster, simpler fitting without electrical wiring
Shared Features
Both the CP4M and CP4B include:
- OpenTherm® compatibility
- Boiler Plus compliance
- Programmable heating schedules
- TPI, Optimum Start and On/Off control modes
- Control of one heating zone
Performance and functionality are the same across both models — the choice comes down to power supply and installation requirements.
Which One Should You Choose?
Choose the EPH CP4M if you have a 230V mains supply at the thermostat position.
Choose the EPH CP4B if you need a battery-powered thermostat with no mains wiring.
Checking this before ordering will help ensure you select the correct thermostat for your heating system and avoid unnecessary returns.
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