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This product is discontinued

Electro-mechanical Programmer

425 series mechanical programmers are the simplest way to control hot water and central heating in the home. The 425 Diadem is a twin circuit, hot water and central heating programmer, with indicator lights and 16 programmes available for fully pumped systems, including independent programming of heating and hot water, and 10 programmes for gravity hot water / pumped heating systems. The Diadem is ideal for gravity systems and fully pumped systems with zone valves.

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Model Replacement
425 Diadem  The above units use the same backplate as H3747 and only require simple wiring changes H3747 or C1727*
* C1727 backplate change and rewire required (economical option)


  •  Control of most domestic gas or oil-fired central heating and hot water systems
  • Combination (‘combi’) boiler systems
  • Stored hot water systems
  • Solid-fuel systems
  • Additional zone control


  • Simple to use with easily understood settings adjustable in seconds
  • All control elements are visually accessible
  • Allows the user to switch the heating Off or on early, without disturbing any existing settings
  • Advanced controls to allow manual overide On or Off
  • Allows the user to pre set a choice of programmes
  • Coronet can be used for loads up to 3kw as well as conventional heating


  • Rotating 24 hour dial and tappet arrangement
  • Easy to install using a nine pin backplate
  • Advance control to allow manual override ON or OFF
  • Programme options: On, Off, All Day or Auto
  • 7 years no quibbles warranty

Technical specifications

Contact rating Double circuit 6 (2.5) Amps 230V AC
Contact type Micro-disconnection changeover voltage-free
Motor Synchronous 230V 50Hz double insulated
Power consumption 2.5W
Dirt protection Normal situations
Moisture protection Ordinary
Enclosure protection Ip20
Maximum operating +55°C
Temperature dial setting 2 On, 2 Off tappets, Min. On/Off period 45 mins
Dimensions 152 x 107 x 39mm
Mounting 9-pin wall fixing plate
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