There is a wiring diagram posted here somewhere but I can't find it. I'll draw it up when I get five minutes, unless someone else posts it.
Replacing complex Horstmann C21 & Drayton Digistat+ with Nest V3
- Thread starter will3h
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- drayton horstmann nest 3rd gen
OK here's my rough drawing:
I dislike them both equally!
Actually in the hundreds of heating systems I have wired, altered and repaired over the years, I've never installed either...
I much prefer Honeywell Evohome, which I also fitted in my own house.
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I should point out that you do not have a gravity/semi pumped system. I assumed, when you said that you had to have the hot water on when central heating was required, that you had a gravity system. Now you have made clear that you have a thermal store, the gravity assumption no longer applies.
In reality, the HW channel on the programmer is being used to control the temperature of the water in the store, not the water coming out of the hot tap - that is controlled by the mixing valve. There is therefore no need to adopt convoluted wiring to make the system work. Flowmax suggest the following:
You have two options – set the "hot water" to constant (24 hour). Alternatively you can set the "hot water" to come on one hour before central heating is required. You cannot have the central heating on without the "hot water".
I have put "hot water" to show it means the store, not the hot tap water.
In reality, the HW channel on the programmer is being used to control the temperature of the water in the store, not the water coming out of the hot tap - that is controlled by the mixing valve. There is therefore no need to adopt convoluted wiring to make the system work. Flowmax suggest the following:
You have two options – set the "hot water" to constant (24 hour). Alternatively you can set the "hot water" to come on one hour before central heating is required. You cannot have the central heating on without the "hot water".
I have put "hot water" to show it means the store, not the hot tap water.
Absolutely D_Hailsham, I agree with you. But the ridiculous point is that currently the Horstmann Programmer in place handles CH and HW separately, which it shouldn't do, and is anyway useless as the CH pump will flow cool water from the store to the radiators. And as it's a rather poor user-friendly device, a smart thermostat would do two things: allow to run it on demand without going and fiddling with the programmer every time the timing doesn't suit our needs (irregular schedules), and wire it to fix the initial situation, and have the HW triggered when CH is required. Reprogramming the whole current thermostat schedules for both hw and ch everytime the outside temp plummets or soars has proven quite annoying.
Soin the case of my thermal store it would be the same wiring as a semi pumped system, as I want boiler & pump to be triggered together, while still being able to control HW separately for summer months.
I realise the topic has drifted a bit... right now I'm trying to wrap my head around this :
Hive is definitely easier to install for my setup and fits on the standard backplate, which will make it a matter of minutes to replace my programmer and bypass the old thermostat, while Nest, with its less standardised heat link will take a bit longer and will require additional drilling on the wall + the schematic that Echo the Husky was kind enough to share.
But on an usage perspective, the Nest still seems smarter, with the Home/away mode based on motion detection, and its learning ability for schedules, plus I guess it's the most "common" system ; while I came to understand that Hive will be programmed like a regular programmer through the app and lacks the "smarts", even if it retains the same remote capabilities and I personally like the fact that the Hive thermostat in itself is powered by batteries making it wireless (even if you shouldn't move it around).
They are both within a £20 price range of each other, which makes it a tough choice.
Soin the case of my thermal store it would be the same wiring as a semi pumped system, as I want boiler & pump to be triggered together, while still being able to control HW separately for summer months.
I realise the topic has drifted a bit... right now I'm trying to wrap my head around this :
Hive is definitely easier to install for my setup and fits on the standard backplate, which will make it a matter of minutes to replace my programmer and bypass the old thermostat, while Nest, with its less standardised heat link will take a bit longer and will require additional drilling on the wall + the schematic that Echo the Husky was kind enough to share.
But on an usage perspective, the Nest still seems smarter, with the Home/away mode based on motion detection, and its learning ability for schedules, plus I guess it's the most "common" system ; while I came to understand that Hive will be programmed like a regular programmer through the app and lacks the "smarts", even if it retains the same remote capabilities and I personally like the fact that the Hive thermostat in itself is powered by batteries making it wireless (even if you shouldn't move it around).
They are both within a £20 price range of each other, which makes it a tough choice.
Don't forget that the store is very well insulated so the heat loss will be minimal. This is why Flowmax suggest leaving the "HW" on all the time - it will only come on when the water in the store has dropped by several degrees, which won't happen unless there is a call for heating or hot water and the store temperature drops significantly. (I can't find any data on the hysteresis of the store thermostat, but it's probably about 10C.)