The EPH CP4 CombiPack 4 is a wireless RF programmable room thermostat and boiler receiver pack, pre-paired out of the box and compliant with the UK's Boiler Plus legislation. It comprises the RFRP-OT thermostat and RF1A-OT receiver — the thermostat sits on a wall or surface in the heated room; the receiver wires directly to the boiler's control terminals. Communication is wireless RF, removing the need to run a thermostat cable from boiler to living area. The CP4 supports four control modes — OpenTherm®, TPI (Time Proportional Integral), Optimum Start, and On/Off — making it compatible with both OpenTherm-capable boilers and standard on/off boiler connections. 7-day, 5/2-day and 24-hour programming, with six time/temperature periods per day. Boost, Holiday mode, and Frost protection included as standard. Expandable to up to six zones via OpenTherm® using a hub receiver configuration.
ℹ Boiler Plus Compliance
The UK's Boiler Plus regulations (Part L, Building Regulations) require that new and replacement gas combi boiler installations include a time and temperature control that meets minimum efficiency standards. The EPH CP4 satisfies this requirement through its OpenTherm® modulation and Optimum Start function — the two principal compliance routes. When connected to an OpenTherm-compatible boiler, the CP4 adjusts the boiler's actual flow temperature in response to real heat demand rather than simply switching it on/off, reducing gas consumption and improving comfort.
Features & Benefits
✔ Pre-Paired — Wire In and Go
The RFRP-OT thermostat and RF1A-OT receiver come pre-paired at the factory — there is no pairing procedure required on site. The receiver is wired to the boiler's OpenTherm or volt-free terminals and the system is operational immediately. This makes the CP4 one of the fastest wireless thermostat packs to commission, with no app download, account creation, or RF pairing steps needed at installation.
✔ OpenTherm® — Modulating Boiler Control
When wired to an OpenTherm-compatible boiler (the majority of modern gas combi and system boilers), the CP4 uses the OpenTherm® protocol to modulate the boiler's output — instructing the boiler to run at a lower flow temperature when less heat is needed, rather than simply cycling it on/off. This reduces fuel consumption, lowers return temperatures, improves condensing efficiency, and extends boiler lifespan by reducing thermal stress from frequent high-temperature cycling.
✔ Optimum Start — Boiler Plus Compliant
Optimum Start calculates how early to fire the boiler so that the room reaches the programmed set temperature precisely at the scheduled time — not before (wasting energy) or after (causing discomfort). The CP4 learns the time required to raise the room temperature by 1°C and uses this to back-calculate the firing time, up to a maximum 3-hour lead time. This is a key Boiler Plus compliance feature and also avoids the energy waste of a boiler running hard for 30 minutes before an occupied period.
✔ Flexible Programming — 7-Day, 5/2-Day, 24-Hour
The thermostat supports three programming modes: 7-day (different schedule every day), 5/2-day (weekday and weekend schedules), and 24-hour (same schedule repeated daily). Each mode allows up to six time/temperature switching periods per day, covering morning warm-up, occupied daytime, lunch return, evening, and setback periods. Boost overrides the schedule for 1 hour; Holiday mode sets a reduced temperature for a set number of days.
✔ Expandable to 6 Zones via OpenTherm®
The CP4 system can be expanded to control up to six independent heating zones from a single OpenTherm boiler by configuring one RF1A-OT receiver as a Hub Receiver. Additional RFRP-OT thermostats in each zone communicate wirelessly to the hub, which relays consolidated demand to the boiler via the single OpenTherm connection. Hot water control can also be added via the CP4-HW-OT accessory.
✔ Smart-Ready — GW04 Gateway Upgrade Path
If the homeowner wants to move to smart/app-based control in the future, the EPH GW04 gateway can be added to the existing CP4 installation — no rewiring or thermostat replacement required. The gateway provides Wi-Fi connectivity and access to EPH's app for remote temperature control and schedule adjustment from a smartphone. This makes the CP4 a low-risk choice that doesn't lock the homeowner into basic controls forever.
Technical Specifications
| Manufacturer |
EPH Controls |
| Product Code |
CP4 (CombiPack 4) |
| Pack Contents |
RFRP-OT (thermostat) + RF1A-OT (receiver) — pre-paired |
| Control Modes |
OpenTherm®, TPI, Optimum Start, On/Off |
| Programming |
7-day / 5/2-day / 24-hour — up to 6 periods per day |
| Temperature Range |
5°C – 35°C |
| Switching Differential |
Adjustable 0 – 1.0°C |
| Sensor Type |
NTC100K |
| Switch Rating |
8A 230Vac SPDT |
| Thermostat Power |
2 × AA batteries |
| Receiver Power |
Mains 230–240V AC |
| IP Rating |
IP20 |
| Max Zones |
Up to 6 via OpenTherm® Hub Receiver configuration |
| Smart Upgrade |
EPH GW04 gateway (sold separately) — adds Wi-Fi/app control |
| Compliance |
Boiler Plus compliant (UK Building Regulations Part L) |
