Immersion Heater Switching

Can Tado please modify the Hot Water Controller. This debacle (on Tados recommendation) has lost me £165.

I sent Tado all tech data and photos for them to study, and on their recommendation I purchased the wireless thermostat starter kit with hot water controller and the wired thermostat from Amazon because it was on offer.

I employed a Tado specialist installer who also had all the tech data and photos to work from.

My installer arrived and began the installation. The wired thermostat was straightforward. But it turned out he could not fit the hot water controller because it only has a single switching capability with a maximum load of 3amps.

Absolutely no use when you have two 13amp 3kW immersion heaters.

I suggested I obtain a 13amp 3kW solid state switching relay but as he was not familiar he refused to even discuss this let alone fit it. But even that would leave the booster heater.

So I'm stuck with the original manual switch, which defeats the whole purpose.

I'm disabled so it was important to me.

I could not return the wireless thermostat and hot water controller kit because I had missed the return window and had used the bridge from the kit anyway, so I had a wireless stat and bridgless hot water controller which was little use to anyone. Stuck it on ebay and lost 70% of what it cost.

So Tado... What a TaDo....

May I suggest you modify the hot water controller or build an additional type specially for modern immersion systems so we can control our two elements...

And please, reduce the cost of a replacement bare bridge.. £85 with no cables or plug... Really?

Also, it would be great to have been able to have the support of Tado in swapping my unused items regardless of where they came from, so I could get sorted out without the major financial loss...

I almost threw my love of Tado out along with all the campaigning I do. I am still extremely sore about the whole thing, especially when I know it's not a difficult job but I can no longer do these jobs myself.
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  • JohnWH


    I would assume that switching two very large inductive loads ( 2 x 3kW immersion heaters = 26 Amps) is well beyond the capabilities of any other manufacturers smart heating controllers as well as Tado.

    Given that immersion heaters are usually equipped with an in-situ thermostat could this provide the necessary hot water temperature control for you?

  • davidlyall

    I agree with @JohnWH on the switching load capability of other manufacturer's products although there are smart products out there that can switch bigger loads (e.g. my Warmup 4iE controlling my conservatory underfloor is capable of switching 16A)

    However, regarding using the immersion's own thermostat, this is not a good idea. I used to leave my HW heating on 24/7 but found that it was continually "topping up" during the day and using far more gas than necessary. I would expect that electric immersions would end up doing the same thing.

    The solution would be to use the tado relay to switch a remote relay/contactor that would manage the full load. Any decent electrician should have been able to advise on that which does beg the question about the installer's qualifications. However, that would only be able to manage a single immersion heater so I'm not sure how Tado would ever have thought they could have managed @Kev3927's dual immersions

  • Kev3927
    I bought all the gubbins recommended by Tado (I sent tech data and photos) to control my electric (hot water) central heating system and the associated immersion heaters (primary and secondary).

    I employed a Tado specialist installer to do the work for me. He too had all the tech data and photos but once he began work he realised the Tado Hot Water controller does not support the 3kW switching capacity, having only a 3amp maximum capability.

    So I ended up with a wired Tado stat (good) and a heap of other stuff that was neither use nor ornament because I had to use the bridge and cables out of the kit (missed the returns window) so I lost about £160...just wasted... I was (am) very unhappy.

    I suggested to the Tado specialist the we get a couple of solid state kW switching relays but because he had never worked with these he refused...but suggested that he set up the manual switch that's already fitted for me. A great help when you want remote hot water programming.

    So I was scuppered....

    So my request is :
    1) to make the Internet bridges more affordable and available with cables.... £85... Really.. With no plug or cables? 🤔 🙄😳😔

    2) modify the Hot water controller so that it has two independent 3kW switching terminals. One for a primary heating element and one for the booster element.

    Or, supply external solid state switching relays with the kits. But intergrated is best.

    Sadly I am well out of pocket, I almost gave up my love for Tado and I still have to clamber in and out of my heating cupboard to switch my elements... Oh so thoroughly modern and easy, especially when you are half blind and physically disabled.
  • JohnWH


    1) Tado do supply cables (Ethernet & USB power), although rather short, with the Internet bridges so am I correct in assuming that you are referring to the wireless receiver which is normally wired directly to the boiler?

    2) Switching 2 x 3Kw inductive loads would require physically large relays which would probably not fit in the existing receiver casings. As such the use of a suitable external enclosure equipped with suitable high current relays would be a better solution and potentially far cheaper than if Tado should ever decide to manufacture one (which in my opinion is very unlikely). Setting this up should be a very simple task for a qualified electrician.

    I hope that you get sorted with a solution which allows use of the Tado stat which you appear to like.

  • Kev3927
    Thank you for your information. When I enquired about purchasing a replacement wireless bridge (expensive) I was informed that no new cables (ethernet or power feed) nor a plug was included.

    My "Smart Home Instalation" electrician categorically refused to fit 3kw switching relays to hook into the hot water controller, it was outside of his experience and as they were not Tado recommended units I was left hanging.

    Unfortunately where I live (not owned by me) I have to get everything fitted and certified by a qualified contractor, else I would have fitted them myself.

    My main issue was having no recourse. Due to Covid and contractor delays I missed the return window with Amazon so could not return the units, and fitting half of the items left me grossly out of pocket.

    My Tado Smart Stat is fitted and works great. It's just frustrating about everything else.

    Thank you.
  • Kev3927
    Using the built in stats is not the option I seek, this would run up huge bills as @davidlyall points out. My desire was to have each heating element controlled via the Hot Water controller App so that I could schedule their on/off times individually and have complete freedom to adjust those times to suit my own requirements.

    The way I saw it working was to have the Tado hot water controller unit switching outputs (3amps) connected to a remote mounted 3kw solid state switching relay(s) which would then switch on/off the heating elements. Simple really and the relays are relatively cheap. <£20
  • JamesU

    I like the core idea of controlling one or more immersion heaters. +1

    But for most people, the Hot Water controller part is used for their boiler, not really an immersion.

    TADO, with more people getting solar there is much more of a market need to offer a unit that can control immersion heaters - with all the same functionality of the Hot Water feature. Solar Systems are much more frequently wired up to a battery and the immersion now to heat water, as that is much better than pushing electrons back to the electric supplier. QED there needs to be a way to manage the on and off the piece, remotely - especially if you are not at home.

    Couple that need with people who actively need to use immersions, like Kev3927, and you have a sizeable market demand for a pretty simple box, with a big relay in it.

  • XKRMonkey
    XKRMonkey ✭✭✭

    @Kev3927 I feel your pain. I may have some help, though it's not strictly Tado centric.

    I have a beef with HW management by many of the so called "Smart" heating systems - they ignore proper hot water management - particularly the problems that the UK market faces (which may not be such a problem in other markets). A summary of my general thoughts and experience is here:

    There are two options that can help you Kev. The simpler option is this:

    It's smart, but uses an app that isn't (or at least wasn't) Alexa compatible. That said, it simply replaces a standard Immersion manual switch, connects directly to your 2.4Ghz WiFi and gives you an app to use to schedule fixed heating periods and boost. I used two of these in the same tank from the app with independent schedules as my first pass at hot water management, before we installed a new Gas boiler.

    Then I discovered SonOff TH10/16 and soon to be TH20.

    These have a sensor port, and you can monitor the temperature of the water in the tank, and then heat it based on genuinely smart scenarios (see the detail in my other post on this topic). You can switch a water solenoid using a TH10, but the TH16/TH20 will switch an immersion heater no problem.

    Because these devices can create smart scenes, you can have them maintain water temperature automatically because they only heat when needed. There is a lot of flexibility and they can be controlled from Alexa/Google etc via the EWELink app. Most importantly, you can manage the energy use because you are heating what you need, not for blind periods "just in case" and with 0.1^ accuracy.

    I notice that TH10/TH16 devices are in short supply right now,. presumably because TH20 will replace them both shortly.

    Feel free to inbox me if you need more help with any of this.

  • edanto
    This is a really valuable thread for me. I’m about to buy a heating control system for our house which currently has radiators (all in a single zone), oil boiler and an immersion with two elements as per Kevs.

    I could see from the Tado website that it was a good fit for the boiler and rads but wasn’t sure if I’d be able to control the immersion.

    This thread really clears it up for me - out of the box the Tado won’t work.

    The idea of a second relay is interesting.

    Would I buy two Tado relays [can the system manage two?], use each one to flip a larger relay that I buy separately and control the two elements in that way?

    Any recommendations for which separate relays I would buy?
  • johnbur
    The best heavy duty 'smart' relay I have found is this (it is z-wave, so needs hubitat, Smartthings or similar):
  • XKRMonkey

    @edanto welcome to the forum.

    Just to re-iterate (based on my earlier post on this subject), there are 2 simple approaches to this, but NEITHER of them include Tado as the controlling agent. Tado's hot water control is limited to the functions of a mechanical timer that is marginally more convenient than 100 year old technology because you can change the settings from your smartphone. (Honestly, separate topic, but for a company that claims to be about energy saving this is very poor - I digress).

    If you want to use a smart timer that can literally replace the manual double-pole fused spur switch in place today (or the manual timer), then you can use Timeguard smart WiFi (no hub needed) Immersion switch. It needs a separate app on your phone, it can switch up to 45 Amps and it's simple enough to configure. Like your existing system though, it will rely on the mechanical in-tank temperature thermostat to shut off demand when temp is reached, and you'll have no idea what temperature the tank is actually at before you jump in the shower.

    Alternatively, Tado could be used for switching large loads using a contactor relay, but you would need a separate 24V or 48V power source to make that work, and you'd still end up with nothing more than a timeclock. The cost of the contactor, a 48v power source and an electrician to wire it together would be more than the Timeguard. Unless you are wed to using a single app, then Timeguard probably wins.

    BUT, Hot water heating is only efficient and comfortable to use when there is a feedback loop (just like the Tado room temperature control), and a mechanism to move away from scheduled heating alone, but to heat on demand when your routine varies or is not in fact routine at all (which defeats time-slot heating programmers usefulness).

    To break away from the last 100 years or so of time-clock mechanisms, look at the Sonoff THR316D or THR320D Elite Smart WiFi controller (this is an excellent update on the older TH16 devices I have used previously for this). It's better in 2 ways, firstly it has an LCD screen so you can see the temperature of the water in the tank, and the cable terminals have been improved so it's easier and tidier to fit). In all other respects it's the same device, it's more ergonomic and less industrial that's all.

    Using one of these, you can set a preferred tank temperature and then when the tank temp drops below a certain threshold, it will automatically reheat your tank to the preferred level. When someone starts showering, the tank cools as cold water replaces the water drawn by the shower, the controller will automatically start heating to bring the tank back to temperature. The next person to shower isn't getting cooler water (depending on your rate of heating of course), so everything is much more comfortable. Yes, you can configure fixed time ON time OFF programmes too, you can even schedule the auto-reheat to only function at key times of the day. Oh, and even the new version is still cheaper than the Timeguard device, even after adding the required DS18B20 temperature sensor.

    The only draw back here, is that there is no fancy app to manage these programmes for you, you will have to do a little thinking and configuring of what you want for yourself.

    The other thing to bear in mind is that you can just as easily use these devices to activate a solenoid to open a boiler flow to a water store, as you can activate an immersion heater, I am using these via solenoids in our UK home, with Timeguards able to operate immersion heaters as a backup, or to capitalise on excess solar electricity available. In our foreign property, we have solar water that has an immersion top-up/auxiliary for winter when solar water may not reach full temperature, the Sonoff THR provides the top-up based on presence (geolocaton) and demand (tank temperature). My Tado hot water schedule is just in permanent "OFF" mode. For immersion switching, the 16Amp or 20Amp versions are required, but for solenoid switching you can use the 10Amp version. Functionally they are all the same apart from the switchable load.

    So Tado (@Jurian and @Rob), take note: The future of hot water heating needs to include temperature monitoring and behavioural response based not just on time of day, but on tank temperature and presence too, regardless of whether the water is heated electrically or by indirect boiler. You cannot claim to be providing energy savings unless you provide a better way to do something than the established norm.

    New hardware should include at least dry contact function to enable the addition of contactor relays as an alternative to mains demand, although the ability to switch high-current mains load such as an immersion heater would be a great option - even if it was a separate expansion module that plugged in to the standard boiler controller (perhaps via a simple expansion cable that plugs into a socket connected to the Hot Water dry contacts on the wireless controller and with it's own separate mains electricity feed capable of delivering at least 16Amps). A modular approach to the hardware requirements of different markets keeps things simple for everyone !


  • edanto

    Thanks Johnbur. I don't have any zwave set up yet (I do have an Apple TV so HomeKit is available to me, but I see that Zwave needs a converter device to work with HomeKit), so I was hoping to find a high-current relay that would be triggered by the Tado relay to have the immersion control fully in the Tado app.

    Sounds like it's possible from the messages above, but I'm not sure yet what relay to source.