Smart TRV's - are they worth it to add to a tado smart thermostat and boiler control?

Thanks for sharing. 

I had these recommended but in my opinion they ( any smart TRV) would only be effective if rooms were isolated from each other by having the doors closed.  TRV’s are after all only fitted to do fine controls in local areas where heat gains may be experienced e.g. a particularly sunny room or a room with high output appliances.  General heating in a house should be controlled by a room thermostat fitted in a room unaffected by such inputs and that room, typically a hallway should not have a TRV fitted at all.   Smart TRV’s will only be effective if the doors between adjoining rooms are closed else temperatures will equalise between rooms through draughts.

I very much question the suggested saving's by TADO which are likely based upon certain conditions and not the average home.  I personally doubt that there’s a payback on their high costs.  I have manually adjusted TRV’s on my radiators and have very rarely ever changed their settings.

The positioning of the room (overall) thermostat matters. It is often placed in the hall, however it is usually best placed where the radiator is least oversized (or most undersized). That way the stat should only drop out when all other rooms have reached temperature. The presence of TRVs in rooms will throttle back the water flow (and hence heating) as each room approaches its set-point, forcing more flow (heat) to the remaining rooms.

I'm not sure what the advantage of "smart" TRVs is. You could fit to bedrooms and turn down the heating during the day but the overall savings are probably marginal.

The energy efficiency improvements from adding a smart thermostat such as the Tado, Hive or Nest is again debatable and I would say are often over-stated.

Our house had a stat in the hall (undersized radiator), however the lounge also had problems heating (end of the pipe run and microbore). The result being that the hall was set much hotter than we liked simply to get the lounge to temperature. We fitted a Hive in the lounge (TRV set to maximum), and turned down the radiator in the hall, hence the system now controls on the lounge temperature. Overall savings maybe 7% to 10%.

A neighbour (same design of house) fitted a Tado in the dining room (radiator 40% oversized). This should have significantly reduced fuel consumption (as they don't use or heat the lounge), however their usage is around 15% higher than before (compensated for weather). The monthly notifications that the stat has saved 8% in the month from using weather compensation are therefore meaningless. I have no reason to believe that the Hive or Nest would have performed any differently to the Tado. I would point out that compared to the conventional (bang-bang on-off) controllers, these smart stats attempt to control the flow temperature by adjusting the on/off duration of the boiler, resulting in often warm radiators. This can lead to the comment that its not working.

Just a bit of personal experience over the years. Thermostats and TRVs can fight each other if you get it wrong. To illustrate this if you have a thermostat in a room and turn the TRVs right down, no matter how hard the boiler works it will never heat the room and every other room will get very hot and you will use a huge amount of energy.

A long time ago British Gas fitted a new boiler and also TRVs to my lounge (the only room they did). The house thermostat was also in the lounge but didn't say how to use them together. When you have a thermostat in a room you don't need to use the TRVs in that room and they should be fully open so that the thermostat can control the room temperature.

I then fitted TRVs to all the other radiators in the house and controlled the temperature locally with the TRVs in that room

If you have a room that is occupied and colder (loses more heat) than any of the others then put the thermostat in that room, fully open the TRV in that room and set the temperature of all the other rooms locally with the TRVs. I bought a wireless thermostat just for that reason and it works very well.

Peter

Hey ​@BeePee ​@Peter E 

Thank you both for your input onto this thread! Very helpful information, and I must say personally, has made me realised just where I could do with one or two in my own home!😀 This might fix the issue I’ve been having without even knowing it.

Just to add that TRVs and gas boilers work well together but not with heat pumps because of the way they work. If you are thinking of installing a heat pump you must discuss the issue of using TRVs because they are not good with the early versions of heat pumps but later versions / different manufacturers may be able to cope with them.

The advice seems to be to use caution when using TRVs with heat pumps. However they can cause issues with gas boilers as well, causing them to "short cycle". In essence as TRVs start to close down, the water flow is forced around the remaining radiators, and the overall flow rate falls.

Now gas boilers have a fairly large hysteresis, probably around 15°C. Boiler systems were generally designed for a delta T (difference between inlet and outlet) of around 10°C, so the hysteresis must be larger than this (when the boiler turns off the outlet will rapidly fall to the inlet temperature and you don't want it switching back on straight away). Steady state, with the boiler running at its lowest heat setting, the outlet would be around 10°C above inlet. If the demand is less than the lowest boiler output then the flow will slowly heat up and the boiler will turn off. However when the system is running at these low flows, and the boiler re-ignites at its high burner setting, then the flow temperature rises rapidly, quickly exceeding the boiler set-point, (before it gets a chance to modulate down) and it switches off. This can repeat several times before it finally manages to catch.

It is also worth noting that even if the boiler doesn't "short cycle" the average flow temperature will be somewhere between the setpoint and the lower hysteresis point. A boiler set to 60°C will thus, in these low load low flow conditions, be providing water somewhere between 60° and maybe 45°C. Since the flow spends most of its time cooling rather than heating, the average flow temperature is probably nearer to 45°C.

Although I (and others) have often suggested running condensing boilers at lower temperatures, this can cause issues as described above.

​@BeePee and there is a difference between how the old bang-bang boilers work (full on/off no modulation) and my new modulating Vaillant. My Vaillant runs the pump slowly (no gas) when the temperature heads downwards towards the set point to sample the return temperature and may come on at a low level to head off the temperature decrease if necessary. I'm sure it has the ability to learn just how much heating to apply on each occasion. Not only are there TRVs in my house but it works in parallel with a heat pump, solid fuel stove and sometimes fan heaters when the electricity price is sub 5p/unit where they are doing most of the heavy lifting on all but the coldest days.

As an aside, last night we had a major HV power cut that disconnected over 4,000 houses in our area. We had the woodburning stove to save the day and led floodlight lamps. I'm never going all electric.

The same return/pump sampling happens with heating the hot water tank. Thus dragging half of the hot water out of the tank during the process which is probably why gas hot water heating is only about 55% efficient and why I can replace it with an immersion heater at a break even cost.

A bit off topic but yes I agree ​@Peter E . The trend towards larger cylinders and larger coils does mean that when the cylinder start to reheat heat is drawn from the top of the cylinder to heat the cooler bottom half.

In many ways the Mixergy cylinder tries to address this by using a coil near the top to heat the water and a small pump to effectively push the thermocline down the cylinder. Unfortunately this doesn’t work well with heat pumps as the return temperature is high (reducing heat pump efficiency).

My home-made cylinder thermostat measures the cylinder temperature at four points. When the heating flow temperature is above the temperature at the top of the coil it opens the cylinder valve allowing the cylinder to heat alongside the heating.

Still wondering about heat pump and EV. Maybe I should share my reasoning for not changing just yet?

Yes. We do have a bit of thread wander here and I'm guilty as charged. I'm wondering if we stop this here to retain the original purpose and head off with another thread with this because it is an illuminating subject but not here. What do you think ​@BeePee ? Shall we head for pastures new?

The query was querying whether there was any benefit in having smart TRV’s instead of standard TRV’s when they already have a smart room thermostat so there has indeed been quite a drift.

If any reader wants to know more about valve types there’s plenty of reading material as well as YouTube videos e.g.  here’s one from the Chartered institute of Building Service Engineers (CIBSE) about different types of valves https://youtu.be/-nUceSN8pXs?feature=shared

Here’s another on smart valves https://youtu.be/YgvKoG-7T30?feature=shared 

I personally have not readjusted any of my manual TRV’s in the last five years at least.  If your system is properly balanced then there’s no need to unless, as I said you can clearly isolate rooms / zones without there being any risk of cross movement of air / droughts.    I have a (non-smart) room stat / timer in the hall (the only room without a TRV) and occasionally change the desired temperature if we’re feeling slightly cold as we keep it quite low for economy reasons.   It has multiple timed periods during each day and I occasionally over-ride that by turning the desired temperature down if we go out.  Reheat time is minimal when we return as the heating is on most of the time.

Two points which I don't think I have made already.

If you make the system too complex to understand how to make it work effectively then you may end up with a worse performance than now. One of my rules is to Keep it Simple. Like ​@Paul4AA I rarely adjust my TRVs but when I do I have tape marking the place where they have to be reset to.

An increase in efficiency may not pay back the cost of Smart TRVs, however, increased comfort may be your aim so that wouldn't be an issue.

Peter

Back on topic…

BEAMA produced a paper estimating the energy savings associated with fitting TRVs. On average this seems to be about 18%.

On a financial basis:-

• Assume annual gas heating bill is around £1000.
• 10 rooms with heating therefore cost per room £100
• Savings per room (18%) around £18 per annum

So fitting a standard TRV (DIY job ~£15 per valve) is probably worth it.

Additional savings from fitting a smart TRV are probably around 10% to 20% on top of the 18%, so an additional saving of around £3 per room per annum. Worth the additional £30? Probably not. As a first fit? Maybe? 

Don’t forget these are battery powered so expect to replace the batteries annually.

And as others have said TRVs are not recommended for use with heat pumps.

I have used both standard TRV’s and smart TRV’s but now only use the standard variety. 
My experiment with smart TRV’s was due to an extension recently built but not in the ‘standard’ flow of the heating in the rest of the house, therefore I thought the smart variety would help to adjust the new location. 
My standard TRV’s are all set to fully open and the system properly balanced as I found that any TRV was at times in conflict with the other variables in the heating system, at times operating against each other. 
With modern systems, so many auto adjustments are made that if additional components try to adjust the flow, you can end up with a poor performance. 
So, in the end I’ve found a well balanced system together with minimal extraneous automations works best .. in other words as others have intimated “keep it simple”.

Thanks ​@BeePee that was a useful document to read. A couple of points. Whereas I'm confident in installing TRVs I don't know many people, apart from plumber friends, who are, so the cost of having them professionally fitted would have to be added on.

There was an also an interesting final paragraph:

------

We therefore conclude that these results should be taken with a high level of confidence. The
installation of TRVs, accompanied by practical advice to householders on how to use them (the
provision of which is already a requirement for installers under the Building Regulations) should be expected to yield significant energy savings across the UK housing stock.

------

The key part is … practical advice on how to use them … As I have said before if you inadvertently have the TRVs set lower than an active thermostat in that room then the boiler will be thrashing away trying to heat the room up without ever succeeding. Perhaps an advantage of Smart TRVs is that the system would never let that happen but are all Smart controllers capable of preventing that situation from happening.

Sometimes we end up buying systens that are sold to save energy but they are too complicated for people to understand so you end up with disappointing results.

Peter

I’ve occasionally considered changing my room thermostat programmer for a smart thermostat, but am not convinced they save what the manufacturers claim, are as reliable as a traditional controller, and I don’t want to be possibly tied into a system that may not always be supported.  However, one of my concerns relates to the poor ways that they’re described / sold. 
 

What I’d like to know regarding the Tado thermostat is how it knows what the outside temperature is because there’s no outside stat in the box and no mechanism for measuring it is described on their web site at all.

I’d similarly like to know how it knows that a window is open as again there’s no door / window contact to measure that.

Hi ​@Paul4AA 

I can only speak of the Tuya app that controls my heat pump but you can select a location for the outside temperature and get it that way. There is an indirect reference to it in this link for Tado.

https://community.tado.com/en-gb/discussion/15768/weather-adaptation

For an open window a local temperature sensor will note a sudden decrease in temperature.

https://support.tado.com/en/articles/3387308-how-does-open-window-detection-work

Peter

Thanks ​@Peter E  which suggests to me that they’re gaining an approximation of the outside temperature from an online published weather forecast rather than a true measurement.  Possibly better than nothing but it won’t be accurate.  It’s similar with the window detection where they’re guessing at a window, or I assume door being open by a more rapid change in temperature than normally experienced.

Such a shame that TADO don’t give this information on their web site including their FAQ’s.

Here’s a Heat Geek article that I’ve just found.

Heres their YouTube video on the subject

Tado just did a BAAAAD thing

They decided to do some market testing and a few days ago (19th February 2025) people logging into the App got a message to say that they would now have to pay £1 a month to access their heating controls. Well, after you had gone though the (as it turned out fake) page entering your card details they suddenly announced: Just testing! It's still free. Which has spooked their customers.

Have a read through this which gives a much more detailed explanation from Louis Rossmann who I follow on YouTube.

https://wiki.rossmanngroup.com/wiki/User_testing_for_mandatory_paid_subscription_into_Tado_Smart_Thermostat_app

I very strongly recommend that you read down to the bottom of the document as to the possible implications of what they have done and the blurred lines between what you might think is your ownership of these devices and a rental agreement.

I've just done an experiment with my Tado smart plugs to see if there is any local control with all the devices and my smart phone on the same WiFi router. Both are still connected to the router.

The answer is no. If you lose your internet connection, not only do you lose any remote control you lose any local control. This means that all control passes through Tado servers all of the time. Unplugging the phone line from the router sends all your devices offline within a minute or two even though the devices are still showing as connected to the WiFi. If you switch off the router the devices show as not being connected to the WiFi (as you might expect).

I'm definitely having second thoughts about expanding my Tado set up although I have just discovered that you can have an internet free system using a Home Hub but even that isn't straightforward.

If I were to consider home automation now then I would be looking for one with native local control without its functionality being dependent on being connected to the cloud except for remote control funtions / operation.

I definitely won’t be buying TADO then as I’m not prepared to be held hostage to a subscription service.  Hopefully I’ll find a similar system where I can use something cheap like home assistant green and retain all of my data and investments.

It's funny but it's events like these that make you realise how little control you have of internet connected devices when it's supposed to give you more control.

I have an EV and I went through a similar experience with trying to sort out a charge point which I thought would be a trivial exercise compared to choosing an EV. Not so. There are very similar issues over control and in the end I built my own dumb charge point as I'm able to do that. It's simple, reliable, cheap, repairable, with the right tariff it saves a lot of money and I have full control over it. It's unfortunate that we have a tendency to overcomplicate solutions.

I hope you find a better solution

Peter