Hi - I have a perfectly functioning CH/HW system controlled by a Honeywell ST9400C. I want to be able to control the CH v HW combinations remotely via an App on my phone from anywhere over the Internet. In addition, it would be handy to have internal on/off time bands available as well although this is not essential as I can already control the radiator thermostats individually this way through Smartlife and Google Home. Does anyone know of a unit that can do this ? Many thanks
'Smart version' of Honeywell ST9400C
- Thread starter Fishman9
- Start date
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You indicate your current system is HW/CH. Is your hot water pumped or gravity feed. Your best bet would probably be Hive or Wiser to replace your ST9400C. However prior to deciding you need to understand your type of heating system. For example Hive supports gravity HW whilst Wiser does not. Pictures of your pump & heating valves should assist in determining suitable paths
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Hi - it is a completely pumped system (in a bungalow) with a hot water storage tank and a motorised three-position valve to select CH/HW output combinations. It is only this function that I don't have 'smart' control over already - the TRVs are all connected via a Zigbee gateway which gives me individual control through the 'Smartlife' app and collective control using Google Home voice-operated routines. The boiler is a Worcester Bosch Natural Gas 15Ri. I've seen the 'Wiser' advertised so will have a look at this first. I've not got near Hive systems yet (as I don't want to get tied in to any one proprietary system) but, again, will have a look. I'm surprised that Honeywell don't market a direct 'smart' replacement for the ST9400c but as far as I can see they don't !? I had a look at the ST9420C but this seems to only be sold as part of a set of thermostatic controls and, even though the components look designed to connect to each other wirelessly, its not at all clear whether the programmer functions themselves can be accessed wirelessly ? May I come back if I have any questions about the wiring implications for the Wiser (or Hive, maybe) ?
If you have a mid-port valve that implies Y-Plan. Presumably you have independent control over HW and CH, some Y-Plan systems require HW to be on to allow the CH to run. As for proprietary systems, they are all to some extent if you tie in their smart TRV's, light bulbs, etc. If however you are just using the HW & CH switching it should not matter which you select.
You should check wiring behind the existing ST9400C, if you have connections to 1, 3 & 4 that's good. In addition there would be the normal L & N and perhaps a connection to an earth tether. If you see no wire in 1 then it's more complicated.
You should check wiring behind the existing ST9400C, if you have connections to 1, 3 & 4 that's good. In addition there would be the normal L & N and perhaps a connection to an earth tether. If you see no wire in 1 then it's more complicated.
Thanks Ian - yes it is a y-plan setup. I replaced the ST9400c with a new one just after we purchased the bungalow around five years ago as very strange things were happening and, since then, its run fine. I do have connections on 1, 3 and 4 so fingers crossed ! Thanks again for your help.
On that basis you should just be able to swap over to either Hive or Wiser. Both use an identical wiring arrangement to what you have today. You may even be able to reuse the current ST9400C backplate but even if not it's a simple rewire.
Just ensure you get the correct model, you will need one providing HW + CH control.
Thanks again - having read through the Hive install and user guides, it's not very clear (to me at least) whether the entry-level 'Hive Thermostat Mini - Model: SLT6' (without a hub in stand-alone mode) gives remote control access at all or whether, if it does, a subscription is required ? Do you know the answer to this ??
No it wont you need the kit, what you are referring to is an add on if you already have the hub, if you have a combi you need the single channel , if you have a seperate HW cylinder you need the dual channel
www.screwfix.com
if you have a combi-boiler
www.screwfix.com
If you have a HW cylinder
yes you can buy cheaper ones but they wont work unless you already have the kit installed, they are add ons to an existing set up
Hive Mini Wireless Heating Smart Thermostat - Screwfix
Order online at Screwfix.com. For use with combi boilers as a new install with smart features. Enables smart heating scheduling, mode, and temperature control via the Hive app. Temperature and mode also adjustable via thermostat touch screen. Features holiday mode, allowing heating control prior...
if you have a combi-boiler
Hive Mini Wireless Heating & Hot Water Smart Thermostat - Screwfix
Order online at Screwfix.com. For use with system and conventional boilers as a new install with smart features. Enables temperature control, heating and hot water scheduling via the Hive app. Temperature and mode also adjustable via thermostat touch screen. Features holiday mode, allowing...
If you have a HW cylinder
yes you can buy cheaper ones but they wont work unless you already have the kit installed, they are add ons to an existing set up
Also note the Hive internet hub uses an ethernet port on your router or switch. I'd recommend you review the differences between the Hivi mini (£108) and regular Hive (£150). The Wiser 2-channel model is also around £150
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The bonus with the hive setup that I have found is that you can add things on. I have 6 lights and one plug socket that can also be controlled remotely (as well as by voice - alexa). Actually, I got the hub and a couple of bulbs first (son gave them to me as he got them free when signing up to an electricity plan and already had his own setup). I then added more bulbs and then got my heating. Because I already had the hub, I only needed the receiver and thermostat and I got those secondhand off of eBay for £25. 
I have Wiser with 5 smart TRVs. Works well. Not sure it is saving me anything TBH.
Mrs McP works from home most of the time. The away mode when she goes out or for holidays and the ability to schedule to turn off away mode via Alexa works well.
I looked into Tado (best looking but requires subscription for some features) and Honeywell Evo (supposed to be the best but looks dated). Wiser was a lot cheaper at the time.
The Hive TRVs have some bad reviews. You may regret going Hive if you want to add their smart TRVs
What have you got as a thermostat?
Could you get a zigbee thermostat and used that to on/off the heating? Won't control the HW
Mrs McP works from home most of the time. The away mode when she goes out or for holidays and the ability to schedule to turn off away mode via Alexa works well.
I looked into Tado (best looking but requires subscription for some features) and Honeywell Evo (supposed to be the best but looks dated). Wiser was a lot cheaper at the time.
The Hive TRVs have some bad reviews. You may regret going Hive if you want to add their smart TRVs
What have you got as a thermostat?
Could you get a zigbee thermostat and used that to on/off the heating? Won't control the HW
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