The Honeywell Home DT4M White OpenTherm Wired Room Thermostat (model DT41SPMWT30) brings modulating, OpenTherm-compatible control to wired room temperature management. Where standard on/off thermostats can only start and stop the boiler, the DT4M communicates continuously with a compatible OpenTherm boiler to fine-tune output, helping the system run more efficiently rather than cycling on and off in fixed steps.
Sharing the same slim, modern design as the rest of the DT4 range, this white wired model can be installed as a standalone thermostat or as part of a wider HCC100 Underfloor Multi-Zone Controller system, and integrates with Honeywell Home evohome for smart zoning. An energy-saving LED display, backlit touch buttons, built-in eco-mode and a temperature boost function round out an easy-to-use, efficient heating control.
OpenTherm
Modulating Boiler Control
White
Colour Finish
Wired
Wall-Mounted Installation
Fuzzy Logic
Control Algorithm
HCC100 Ready
Multi-Zone Compatible
5 Year
Manufacturer Warranty
OpenTherm & OpenTherm Smart Power Support
DT4M versions support OpenTherm-compatible appliances, with variants available for both standard OpenTherm and OpenTherm Smart Power, which draws power directly from the boiler connection so batteries are not required for that variant. Confirm which OpenTherm variant matches your boiler and installation before ordering.
Qualified Installation Required
This thermostat wires directly into the heating appliance's control circuit. Installation should be carried out by a qualified electrician or heating engineer in accordance with current UK wiring regulations and the manufacturer's instructions.
Not for Electric Heating Circuits
The DT4M is compatible with 24-230V on/off and OpenTherm appliances such as gas boilers and combi boilers, and also works with zone valve applications, but is not suitable for 240V electric heating circuits.
Modulating OpenTherm Control
Continuous communication with a compatible OpenTherm boiler allows the appliance's output to be modulated rather than simply switched on and off, supporting steadier room temperatures and potentially lower fuel use.
Standalone or Multi-Zone Ready
Can be installed as a standalone thermostat, or as part of a wider HCC100 Underfloor Multi-Zone Controller system for room-by-room zoning.
Smart Device Integration
Integrates with Honeywell Home evohome and the HCC100 Underfloor Multi-Zone Controller, extending the thermostat into a broader smart heating setup where needed.
Built-In Eco Mode & Boost Function
A built-in eco-mode reduces room temperature over a set interval to save energy, while a temperature boost function allows a temporary increase when extra warmth is needed.
Energy-Efficient LED Display
The LED-based display is easy to read and automatically turns off when not in use, helping conserve power without sacrificing visibility when needed.
Guided Installation Support
The thermostat is supplied with an installation guide including a QR code linking directly to installation videos, helping installers get set up quickly and correctly.
General
Model / MPN
DT41SPMWT30
Product Family
DT4M OpenTherm Wired Room Thermostat
Colour
White
Installation Type
Wired, wall-mounted
Installation Modes
Standalone or part of HCC100 Underfloor Multi-Zone system
Compatibility
Boiler Compatibility
OpenTherm and OpenTherm Smart Power (variant dependent)
Appliance Compatibility
24-230V on/off and OpenTherm: gas boilers, combi boilers, heat pumps
Smart Integration
Honeywell Home evohome, HCC100 Underfloor Multi-Zone Controller
Not Compatible With
240V electric heating circuits
Control & Display
Control Form
Fuzzy Logic
Switching Capacity
3A (Resistive), 1A (Inductive)
Switching Type
SPDT
Sensing Element
10k NTC thermistor @ 25 °C
Room Temperature Display Range
0 °C to 40 °C
Display
LED, auto-off, backlit captive touch buttons
Energy Features
Eco-mode, temperature boost function
Power & Warranty
Power (Standard OpenTherm)
2 x AA batteries
Power (OpenTherm Smart Power)
Powered via boiler connection, batteries not required
Warranty
5 years
What is OpenTherm and why does it matter?
OpenTherm is a communication protocol that lets the thermostat and boiler exchange information continuously, allowing the boiler to modulate its output to match demand rather than simply switching fully on or off, which can improve comfort and efficiency on compatible boilers.
Do I need batteries for this thermostat?
Standard OpenTherm versions run on 2 x AA batteries. The OpenTherm Smart Power variant draws power directly from the boiler connection, so batteries are not required for that version - check which variant you have.
Can this thermostat be used with a multi-zone system?
Yes, the DT4M can be installed as a standalone thermostat or as part of a wider HCC100 Underfloor Multi-Zone Controller system, and also integrates with Honeywell Home evohome for smart zoning.
Is this compatible with my boiler if it's not OpenTherm?
The DT4M also supports standard 24-230V on/off control in addition to OpenTherm, so it can work with a broader range of gas and combi boilers, though it is not suitable for 240V electric heating.
What does the boost function do?
The temperature boost function temporarily raises the room temperature setting for a set period, useful for a quick top-up of warmth without adjusting the full schedule.
BTU & WATT Calculator
Room Dimensions
Room Type
Living Room
Bedroom
Kitchen
Bathroom
Conservatory
Hallway
Glazing Type
Single Glazed
Double Glazed
Triple Glazed
External Walls
0 Wall
1 Wall
2 Walls
3 Walls
4 Walls
Insulation Level
Poor
Average
Good (New Build)
Required Heating
0
Watts
0
BTUs
Documentation
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