425D Diadem Central Heating Programmer5015914551017425 Diadem

Width: - 152mm
Height: - 107mm
Depth: - 39mm
Horstmann 425D Diadem Programmer
  • This twin circuit, hot water and central heating programmer, with indicator lights,
  • 16 programmes available for fully pumped systems, including independent programming of heating and hot water
  • and 10 programmes for gravity HW/pumped CH systems. Programmes allow permanently ON or OFF, On all day or ON/OFF twice a day.
  • An advance switch gives temporary override without altering settings.
  • The Diadem is ideal for gravity systems and fully pumped systems with spring return zone valves.


Horstmann Data & Wiring Sheet + Compatability list
Order Code
Price (ex VAT)
Price (inc VAT)
product photo

HO 425D

425D Diadem Central Heating Programmer Extended Range*


EA 3+




EA 3+