Replace Danfoss Randall 4033 with Tado Extension

31 Dec 2020
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United Kingdom
Hi, this is my first post, so pardon my ignorance.

I've not been too long at this new bungalow for my parents, there is a Danfoss Randall 4033 timer for Hot Water and Heating (click the link for pictures: It looks really old and for some reason, it's been mounted about 6.5 foot up the wall inside a cupboard, hence my father who is 83 has to climb onto a chair to turn on/off the unit..... blooming nightmare and extremely dangerous at his age.

IMG_8705.PNG IMG_8707.JPG

I did manage to replace the thermostat with a wireless Tado unit, which works well, but the hot water switch on the timer still needs to be controlled manually. So I've placed the order on Amazon for the Tado Extension box and that's due to arrive soon and I wanted to plan ahead to get it installed.

The Danfoss Randall 4033 has 4 or 5 wires entering the unit and wanted to know how the Tado Extension Box would be wired up?

I have a conventional Vaillant boiler with a water tank in the loft.


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Google "vaillant eco TRC plus 428 installation instructions" and it shows this boiler uses a connection to the ebus, as with most modern boilers there are many ways to control it, so can be simple on/off, however I would suspect you want it controlled in an economic way, so the question is how much do you want to spend.

Not being funny, but some of the systems can cost £1000's and at 83 he is unlikely to get that money back in fuel saving, I looked at Tado and rejected it due to lack of information about their product, I fitted Nest Gen 3 and that was jumping out of frying pan into the fire, as then found they had removed the support for the TRV heads.

In the main system boilers with on/off control are switched on by a micro switch in the motorised valve and the thermostat works the valve, but we have S Plan, C Plan, Y Plan, and W Plan and variations with the plans, without knowing how already wired it would be impossible to say how it can be altered.
I thought Tado was opentherm? I know there is one system that uses opentherm with master and slave set up. Think three letters some think like EPH so it uses both contacts to control the motorised valves and opentherm to control boiler, however since my boiler not opentherm not really looked into it. But at 83 would expect you want some thing easy to use, although my Nest has some faults, I must say easy to use, simple dial to turn heating up/down and large display to show setting. Setting the domestic hot water not quite as simple, but I never alter that any way, and you could do it for him.

But how much do you want to spend.
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My dad uses the Tado app and he can turn on the heating and change the temperature up or down, so adding the Hot Water Controller would be ideal.

How do I figure out what S, C, Y or W plan configuration/variation I have?
what motorised valves do you have determines what system you have
  • Thanks
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Have a look in the cylinder cupboard, if you don’t know how many valves you have, post photo of cylinder cupboard

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