How to replace a zoned Honeywell CM707 wired thermostat system to a Tado Smart Wireless Thermostat?

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I have a Honeywell zoned thermostat system with an Ideal Logic Combi boiler. There is a wired thermostat in the front entrance room that controls all the hallways and the downstairs rooms and another wired thermostat in one of the bedrooms which controls all the upstairs rooms and bathrooms. These are controlled by the radiator switch valves in one of the airing cupboards in one of the bedrooms that looks like this:

I have bought a Tado Wireless Thermostat Starter Kit and I have installed the wireless receiver to the boiler and paired the wireless thermostat to it.

The boiler is sending an L1 error (lack of water flow) whenever heat to radiators is requested which eventually leads to no hot water in even the taps. I have realised that there is more to do:

- The wired Honeywell thermostats need to be decommissioned. Is this correct? If so, how do I do this? This is how the existing wiring looks:

Downstairs

Upstairs


- something needs to be done with the 2 switch valves in the airing cupboard that control the flow to the each radiator zones. Is this correct? What needs to be done?

End goal

The end goal is to remove the existing zoning for heating with the HoneyWell thermostats and the switch valves (i.e. the entire home temperature controlled by the new Tado wireless smart thermostat which will be placed in the living room). I will also be installing Tado smart wireless radiator valves to 4 of the rooms which will have their own temperature control.

I’m not an Engineer and so this is a DIY project for my own home so any advice in laymans terms would be extremely helpful.

Answers

  • davidlyall
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    So, it sounds like the way you've set it up, the valves aren't opening so you're not getting flow

    You have two options

    1. Fully remove the valves and replace with straight pipe. This will also need wiring changes as right now, the wall thermostats control the opening of the valves. Once a valve is open, it then triggers the boiler and pump to run
    2. Replace the wall thermostats with Tado wired thermostats so you retain the valves and the Tado thermostats are the zone controller for each zone. They will be a straight replacement with no wiring required

    Personally I'd go with option 2 as it's almost guaranteed to be cheaper to implement and will still retain the two zone pipework. This will reduce heat losses slightly as you'll only be pumping heat around the circuit that needs it. It might also make it slight easier to integrate Tado radiator valves at a later date

  • tarekahmed
    edited August 2023
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    Thanks for your response @davidlyall

    I was told that I can bridge the wires to decommission the zoned wired thermostats which will give the wireless thermostat full control over the heating and always keep the valves open. Does this sound correct? Are you aware of how I can bridge the wires on the above two thermostat pictures?

  • johnnyp78
    johnnyp78 ✭✭✭
    edited August 2023
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    I would either do what David suggests or get an electrician in to bridge the wires - presumably meaning short the valves so they're always open. It's not worth messing with live current if you're not sure what you're doing.

  • tarekahmed
    edited August 2023
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    Thanks for your response @johnnyp78

    The thing with option 2 of @davidlyall ’s comment is that it means the 2 zones will remain. I would like to get rid of the zoned system and place smart radiator valves to control zoning.

    I know how to bridge the wires but is it the black and brown wires that I’d need to bridge?
  • johnnyp78
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    By installing wired thermostats on to the heating valves you will effectively be getting rid of the zones, though it will cost you more. Not sure about the wires I’m afraid but perhaps someone else here can help.
  • The way that I had resolved this was by turning both of the heating valves located in the airing cupboard to ‘manual open’ which keeps the valves open at all times across the entire house.



    The wires that come into the wired thermostats just control this opening and closing automatically. So I’ve also bridged those (although there was no charge running through it having tested it with a phase tester). I’ve just bridged those as instructed by the Tado manual: