The ESi ESRTP4+ is a wired programmable room thermostat that combines time and temperature control in a single wall-mounted unit, without a separate RF receiver to install. It provides the same core energy-saving intelligence as the wider ESi programmable range, including Chronoproportional Control (TPI), Delayed Start, Optimum Start, and Optimum Stop, alongside an OpenTherm interface for compatible boilers.
Wired directly into the heating circuit via volt-free changeover contacts, the ESRTP4+ suits installations where a hard-wired thermostat is preferred over an RF-paired system, while still offering full 7-Day, 5/2-Day, or 24-Hour programming with 4 or 6 daily events.
7/5-2/24h
Programming Modes
4 or 6
Daily Time/Temp Events
5-35°C
Temperature Adjustment Range
±0.5°C
Sensor Accuracy at 20°C
6(2)A
Total Switch Rating
Installation requirement: This unit must be installed by a suitably qualified person in accordance with the latest IEE Wiring Regulations (BS 7671) and Part P of the Building Regulations. The mains supply must be isolated before commencing installation, and the fixed wiring connection must be via a fuse rated at no more than 6 amps with a Class 'A' switch providing a minimum 3mm contact separation in all poles.
Cable sizing: ESi recommends 1.0mm² or 1.5mm² cable for the wired connections. Actual cable sizing must be calculated by a qualified electrician in accordance with BS 7671, based on the specific installation and circuit conditions. No earth connection is required, as the product is double insulated, though continuity of earth must still be ensured throughout the wider system.
Chronoproportional Control (TPI)
TPI fires the boiler at regular, adjustable intervals rather than simple ON/OFF switching, matching boiler heat output to the building's actual heat loss. This reduces boiler cycling and return water temperature, improving overall system efficiency.
Delayed Start & Optimum Start
Delayed Start can push the next programme's start time back by up to 45 minutes based on room temperature, while Optimum Start calculates the ideal pre-heat time automatically so the home reaches its target temperature exactly when scheduled, without manual guesswork.
OpenTherm Compatibility
Where connected to a compatible OpenTherm boiler, the ESRTP4+ supports polarity-free OpenTherm connections with a maximum line length of 50 metres and maximum cable resistance of 2.5 Ohms, enabling features such as load compensation and configurable domestic hot water settings.
Installer Lockout Modes
Five selectable lockout levels let an installer restrict end-user access, from a fully open default setting through partial lockouts that fix a maximum temperature setpoint, up to a full lockout where no end-user adjustment is possible, useful in rental or shared-occupancy properties.
Landlord Service Reminder
A configurable service interval feature displays a SER warning up to 30 days before an annual service is due, with optional settings that progressively restrict daily heating run-time once the due date has passed, encouraging timely safety servicing.
Hard-Wired Reliability
As a fully wired unit rather than an RF-paired system, the ESRTP4+ removes any dependency on wireless signal strength or RF handshake intervals between thermostat and receiver, suiting installations where a direct wired connection is preferred.
| Programmable Room Thermostat |
| Programming Modes |
7 Day, 5/2 Day & 24Hr |
| Power Supply |
2 x 1.5V Lithium AA batteries |
| Temperature Sensor Accuracy |
±0.5°C at 20°C |
| Temperature Adjustment Range |
5°C to 35°C |
| Total Switch Rating |
6(2)A 230VAC |
| Contact Type |
SPDT volt-free changeover |
| Maximum Load |
1380W |
| Number of Programs |
4 or 6 (default: 4) |
| Events per Day |
4 to 6 |
| Protection Rating |
IP30 |
| Dimensions |
127mm (L) x 81mm (W) x 28mm (D) |
| BST/GMT Time Change |
Automatic |
| Casing Material |
Thermoplastic, flame retardant |
| OpenTherm |
| Connections |
Polarity free |
| Maximum Line Length |
50 metres |
| Maximum Cable Resistance |
2.5 Ohms |
| Wiring Terminals |
| Terminal 1 |
N/C - Normally Closed |
| Terminal 2 |
COM - Linked Live Feed (230VAC heating applications only) |
| Terminal 3 |
N/O - Normally Open |
| Compliance |
| EC Directives |
EN60730-1, EN60730-2.7, EMC 2014/30/EU, LVD 2014/35/EU, 93/68/EEC |
Does the ESRTP4+ require a separate RF receiver?
No. The ESRTP4+ is a wired unit connected directly into the heating circuit via its N/C, COM, and N/O terminals, unlike the RF-paired ESRTP4RFW, which uses a separate wireless receiver.
What cable size should be used for installation?
ESi's guidance recommends 1.0mm² or 1.5mm² cable, but actual cable sizing must be calculated by a qualified electrician in accordance with BS 7671, based on the specific circuit and load.
How many temperature events per day can be programmed?
The thermostat defaults to 4 daily programs but can be reconfigured to 6 daily programs via the technical settings menu, giving up to six separate time and temperature changes each day.
Can an installer restrict what the end user can change?
Yes. Five lockout modes are available, ranging from full end-user access through several partial lockout levels (which fix a maximum temperature setpoint) up to a full lockout with no end-user adjustment permitted.
Is this thermostat compatible with OpenTherm boilers?
Yes. The ESRTP4+ includes an OpenTherm interface with polarity-free connections, supporting a maximum line length of 50 metres and maximum cable resistance of 2.5 Ohms, with configurable parameters including low load control and domestic hot water settings where the boiler supports them.
