Changing Ideal Logic Max S30 to Opentherm

johnbur

Hi, we had this boiler and Tado fitted nearly four years ago and all has worked really well.

However, reading these forums, I see that there could be advantages to changing from relay to opentherm.

We have the UK extension kit with opentherm connections, so should be possible?

My question is, are the advantages worth it given that all is working fine at the moment? - don't want to break anything 😱

Also, is it just a wiring change, or do Tado Support need to change anything at their end?

Many thanks

Rob2

There are 3 changes you need to make:

1. wiring of the extension kit to the boiler (see boiler manual), different connection points
2. wiring of the extension kit itself (different connection points, +/- instead of COM/NO)
3. configuration of the Tado system (see installers manual or ask support

Advantage of OpenTherm is that it provides modulation control of the boiler, so it can run at lower output instead of being toggled on/off. That results in better efficiency and less temperature variation around the setpoint.

johnbur

Many thanks @Rob2 - do you think that it will be worth doing?

johnnyp78

It’s definitely worth doing (and easy to do) and as you said your kit has opentherm support. But … see my next post

johnnyp78

Rob2’s instructions are pretty clear. Are you comfortable taking some wires out of your boiler ‘chocolate block’ and putting them in somewhere else, and doing the same on the extension box? That’s all there is to it. You might need to update the smart thermostat but mine recognised it was Opentherm automatically.

Having said all that, I think you have a system boiler (separate hot water tank)? Unless it’s a combi you’re best leaving as it is.

Rob2

Yes, the wiring is easy to do. But remember you also need to change the Tado configuration.

You can do it using the configuration wizard at https://tado.com/start and answering the "what is your old thermostat" question with a random OpenTherm type like the HoneyWell T87M. Or you can download the installer manual there and use the installer configuration on the Tado thermostat, selecting protocol D01.

johnnyp78

Going to emphasise again that if you’ve got a system boiler with a separate hot water tank - installed in the uk way with y or s plan, you won’t be able to switch to Opentherm without giving up control of the hot water. However, EU installations seem to get round this, so there’s a slim chance it might still work.

johnbur

Many thanks both. If I do it, the installer who originally fitted the boiler is happy to make the changes, so I won't be touching anything!
You are correct - it is a system boiler, so disappointing that it won't handle the hot water.
Not a big deal though - what would be needed for hot water control?

johnnyp78

I would quite like to know this myself. I know that the UK (and possibly Ireland) is the only place that uses S and Y plan for hot water tanks, so presumably in most EU countries there’s a different installation method that allows the hot water to be controlled with Opentherm rather than 230v relay. Maybe someone else can spread some light on it.

Rob2

Over here in the Netherlands, the usual setup is only doing flow heating. So no big water tank.

Older boilers have a 1-3 liter tank (combined with heat exchanger) that can keep a small supply of hot water, and the Tado hot water control switches that heating off or on. In many boiler types, when it is off, it just means it takes a bit longer to get hot water at the tap because everything has to start from cold. The OpenTherm bus can send a command to do this switching.

On more modern boilers (with highest efficiency rating) even this small tank is no longer present and the hot water is heated directly in the main heat exchanger, which has a separate circuit for that (to keep the tap water separate from the heating water). This requires even less pre-heating. I have such a boiler and I have configured Tado not to control the hot water at all, it is just off until I open a tap.

johnnyp78

So you basically only use combi boilers? Interesting. How does that work in large houses or households with high water demand? Seems like a much easier set up to deal with though than s and y plan.

Rob2

There are different classes of boiler with different hot water capacity. You need to choose the right one for your demand.

But of course the hot water capacity is never what a large tank can supply. I remember when in my house at that time the large tank was replaced with a combi boiler and it took a lot longer to fill a bathtub.

There probably still are installations with an external tank, they just aren't very common. In my family nobody has one.

GrilledCheese2

@johnbur for OT to work your boiler needs to know both the room and cylinder temperatures. if your hot water cylinder has a regular on/off thermostat then you won't be able to use Tado in OT mode. A thermostat with a small dial to set the water temperature is quite likely to be the on/off type. You cannot have this on/off switch in combination with OT for the radiators.

If your cylinder has a temperature probe that communicates the water temperature in the cylinder to the boiler then it might be possible to use OT with the right OT controls. I have no idea if your boiler supports this mode of operation, but a good plumber should be able to work it out from the boiler's installation manual.

johnnyp78

Not sure if I should be advertising rival systems on here, but looks like Evohome and ideal’s own touch system both support 230v and opentherm simultaneously, so that might be the route to go down, but tbh if you don’t want the expense and hassle of switching from Tado I’d stick with what you’ve got.