Interlock of hot water and central heating?


I've replaced a Horstman 425 Diadem programmer on my gravity fed hot water and pumped central heating, following the instructions Tado provide.

A key pecularity of the Horstman programmer was the way in which the hot water and central heating operation were interlocked, as described by its manual:

"If a Diadem ... is used on Gravity Hot water/Pumped Central heating systems the selector slides must be interlocked for correct programme selection..

Check for correct operation of programme slides. This should result in the HW selector moving up to match any CH selection (twice, all day and 24 Hours). When the CH slide switch is returned to any of the lower position (all day, twice and off), the HW slide switch will stay in the uppermost position reached and will have to be manually moved to the desired new position."

Is there a way to get Tado to perform the same interlock? So if radiator heat is demanded, the hot water is turned back on? Without this demand for hot water, the central heating simply doesn't run. Likewise I need the Early Start feature to turn on the hot water early to match the radiators.

Best Answer

  • xfield
    Answer ✓

    I did some more digging, and found this instruction manual: which lists lots of codes for the relays and hot water settings. Then following the installation instructions for the wireless thermost, I changed the relays from R01 to R02. This has made it work and I can now set the hot water to follow a programme. Meanwhile central heating can demand heat whenever, and will also turn on the hot water whilst heating is on.


  • If you’re using the extension kit or wireless receiver then I believe both can be configured for a gravity HW system. You’ll probably need customer support to make the config change for you.

  • I have the extension kit - I'll give customer support a try. 👍️