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Multi zone help

Hi members, I've had an issue with an install of my tado smart system, I tried searching but can't find the right response.
I have two heating zones in my house, upstairs and downstairs on separate valves to the water tank. I had the smart thermostat installed and have the wireless one downstairs, but left the existing wired one as is for upstairs. My issue is that the upstairs heating will only come on if I also have the downstairs heating on at the same time. Should I replace the upstairs thermostat for a tado wired one or can I use a wireless one like downstairs?
Thanks for any help anyone can offer