Buying correct Tado system for our setup

mattjonesuk

We currently have a two zone (upstairs and downstairs) system with wired thermostats in each zone and basic TRVs in each room except the ones with the thermostats. At the boiler end we have, I think, two mechanical zone switches wired to an Ideal Logic Combi ESP1 35. The issue I have is that the bedroom with the upstairs thermostat gets warm quickly meaning that the heating cuts off and the other bedrooms are freezing. So my plan is to install smart TRVs to every radiator and then also get a smart thermostat so that the cold bedrooms can override and keep the heating on until they are warm enough.

So according to Tado shop I need a wired starter kit and another wired add on thermostat, plus the smart TRVs. However, I think I would be better off overriding the two zone system and just having one zone with each room being controlled individually by the smart TRV. So does anyone know if I can just manually override the each mechanical zone (so they are constantly calling for heat) and then buy one thermostat and wire this directly into the OpenTherm terminal on the boiler to actually control the boiler? If so, do I want a wired thermostat (?) as I assume that the current thermostats are wired directly into the mechanical zones rather than the boiler? Am I better getting a wireless thermostat and wiring this into the boiler and then just covering up the existing thermostats?

Hope that makes sense!

mattk86

Hi, if anyone has any advice on this I would also be interested - as have pretty much the same set up and same boiler. I have two zones, with wired Honeywell thermostats connected directly (I presume) to the zone valves in the upstairs airing cupboard which then ask the boiler for heat when opened.

Ideally I would like to replace the existing thermostats whilst maintaining the zones and use Opentherm, if that is at all possible. I understand otherwise I could use two Tado wired thermostats to simply replace like-for-like the existing Honeywells, remaining in relay on/off mode.

mattjonesuk

Hi @mattk86

Hopefully someone will come back with a response. I think I’ve worked out that it is possible to have opentherm on two zones (essentially the zone with the highest demand takes priority I think). You’ll need two smart thermostats though. My preference is to get rid of the zones and replace with smart TRVs, as this will give me more granular control than the zones and better efficiency. I believe you can just wire in the Tado wireless receiver to the OpenTherm and then take a power supply from a 230v supply. Beforehand you need manually open both zones (there should be an override on the valve itself) and disconnect the from the stat terminals in the boiler. I’m hoping then the boiler will operate based on opentherm and Tado, and both zones will be open so when the boiler is on then both zones will have heat. Then each radiator can turn off when needed. I’m getting a quote from a heating engineer to do it I think.

wateroakley

Hello @mattjonesuk Welcome. In principle: For simplicity of fitting I'd suggest you go for the two wired thermostats (wired starter kit and an extra wired thermostat), and add TRVs on the radiators. If the location of the wired room stats is unhelpful for measuring the room temperature, you can add a wireless temperature sensor. You can set the bedroom TRVs to 'call for heat' when they need to be warm. When adding TRVs, always check if your boiler needs to keep an external 'bypass' from a radiator without a TRV.

Hello @mattk86 Welcome. In principle: If you are using 'relay' connection, either the same as above, or a wireless starter kit and one wired thermostat, and add TRVs on the radiators.

Both: It's best to check with the above with the Tado support people from the main web site chat.

Sorry, I don't now much about how your Opentherm would be re-wired and function with the zone valves. For most 'users' re-wiring adds unneccessary complexity to the install.

This graph below shows our monthly results for the same outside temperature with 'relay' and TRVs with a 13 year-old Baxi boiler that modulates. No promises that the same results can be achieved by others.

Good luck with whatever you decide to do.