Smart thermostat for dual zone district heating

22 Sep 2015
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United Kingdom

I'm after guidance on which smart thermostat will work with my district heating system. These are still not that common, so struggling to get a factual answer.

My current system (photos attached):
* 2 zone system, each with a programmable thermostat. One to bedrooms and another to living areas
* I only need to control heating with thermostats. Hot water is delivered without control straight from HIU
* Current thermostats are battery powered Wolseley Centre EHE0200 (153|154) with 2 wires (L & N) connected
* I have 4 core wires running from the thermostats to a junction box next to HIU. 3 wires (2 connected to L & N on the thermostat, 1 spare). 1 yellow green earth connected to metal back box behind the thermostat
* From the junction box, cables go up to 2 x Drayton zone valves (both currently set to Auto)
* Simply, when each thermostat wants heat, the respective valve is opened, the HIU comes on and hot water travels to the radiators
* Radiators are a mix. Some standard, and some have manual TRVs

My questions:

1. Since there is no boiler, can I set the Wolseley thermostats to Manual i.e. ON at all times, and replace the manual TRVs with smart TRVs and control heating that way? I think the answer is no, because the the thermostat will be telling he HIU/valves to pump water at all times, while the TRVs will be shut when I don't want heating. Doesn't seem it will work, but tell me otherwise.

Assuming I do in fact need to change to a smart thermostat (regardless of TRVs):

2. Even though I have an HIU, is my system/thermostat equivalent to what's known as a 2 wire system? i.e. just L and N?
3. Between Hive, Nest and Tado, which would be compatible?
4. Are there any other cheaper, or non subscription based smart thermostats I could use? I was interested in Meross smart thermostat, but it doesn't appear to support 2 wire systems

Any advice appreciated.


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Forgot to add that the HIU also has an actuator. A Honeywell M6410l2023. Not certain if that is used for heating or hot water, or both!


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