Another Nest Install - Can someone check my wiring?

[sparkymark75]

Not sure if this should go in here or the Plumbing and Central Heating forum, but here goes anyway.

I have the following components in my new build house;

• Ideal Logic Combi ESP1 35 Condensing Boiler
• Honeywell Frost Protection (L641B1004)
• Honeywell Outdoor Temperature Sensor (SO10076)
• 2 x Danfoss TP5000 Thermostat/Programmer

Both of the TP5000's are wired back to a wiring box at the boiler. I've reviewed the wiring in this and diagrammed it to trace what goes where. I've attached this and another diagram of my proposed changes. I'd appreciate it if someone can give it a once over to see if it looks okay.

The wiring for the TP5000's is buried in the walls and only surfaces right next to the wiring box. So this means I'm going to need to feed the 240v to the Heat Links from the wiring box and then the 12v from the Heat Links back to the wiring box and then back to the Nest controllers.

Thanks.

 

[ericmark]

It would seem the two thermostats are wired in parallel, I can see with old thermostats how you may want two to bring on the boiler, in fact that is what I have with mothers house, however whole idea of Nest is they integrate with eTRV's and other devices using the ITTT system. So question is why two thermostats?

Some times you have to stand back and ask, what is that for? So with a modern house the boiler is condensate type which means the flame varies in height, the radiators are fitted with TRV's so the TRV's tell the boiler either by return water temperature or back pressure what flame height is required keeping the house at the set temperatures for each room with a seamless variation of boiler output.

However as the weather warms up the boiler starts to cycle, so at some point you need something to turn off the boiler, there are exceptions with open plan houses, but in the main that's how it works, so in some room (that could also be a hall) you fit a thermostat to switch off the boiler as the weather getting warmer, this needs to be a room with no other forms of heating, with no doors to outside and the coolest in the house.

In my house there is no such room, so to keep down installation cost I have used two thermostats, one in hall, one in kitchen, the latter is only active over night, and the temperature in the hall stays static there is only two options, on or off, the temperature is matched to the TRV so is never altered.

To jump to next stage of control means linking a Nest or Hive to the eTRV's with follow commands, to be frank, simply no point in taking this half hearted approach, either you want the eTRV to connect to a hub which in turn controls boiler, so if any eTRV reports target is greater than current then boiler runs, in which case you don't need a wall thermostat, or some other form of zone control. So thermostat controls a motorised valve which in turn controls boiler, so you can set it so upstairs and downstairs are independent.

Now you show two zone valves, which at first glance seemed fine, but one seems to be controlled by something labelled "Mains" and the other by the two thermostats. Zone valve 2 seems to be controlled by both thermostats, and zone valve 1 by "Mains" what ever that is, I will guess cylinder stat?

Now for a non programmable thermostat have two at different temperatures with a time switch to select one for night and one for day makes some sense. But the Danfoss TP5000 Thermostat/Programmer is a complex unit and I can't work out why you have two? I also can't see an advantage using Nest? the Danfoss TP5000 Thermostat/Programmer has all sorts of gadgets, from window sensing to switch off central heating if window is opened to sensing outside temperature, unless you up graded to something like EvoHome there would be little point changing anything.

I will admit I made an error, I got MiHome eTRV's which OK I can access from phone and change the temperature in the house from other side of the world if I want, but why would you? In real terms once set, they stay as set for whole of winter, so I could have bought so half the price and done the same thing as I do now, only when you get the type which connects to a central hub do you get any real advantage.

And if you can alter the temperature of each room, why do you need a thermostat to set all temperatures? Yes with the follow command you can have either the Nest follow the eTRV or the eTRV follow Nest, but why? whole idea is each room is independent so why then connect all together?

So think what do I want to do, then design a system to do it. At home with an old open plan house Nest would work fine, in mothers house with internal doors, waste of time.

 

[sparkymark75]

With my diagrams, I made an assumption as to what the source of the cables coming into the right side of the junction box was. I may have this wrong. What is the easiest way to check this?

The top two grey cables I assumed were the TP5000s as they are both 3 core & earth, matching the wiring at the TP5000 end. The power cable for the boiler is white, so I assumed the white cable was the boiler. The bottom grey cable I assumed was the 240v power supply (mains). You can't see it in the photo but behind the bottom grey cable, there's another grey cable, a twin and earth. I'm not sure what this is.

By mains I meant 240v power supply. I don't have a water cylinder.

I have TRVs on all the radiators with the exception of the two rooms with the TP5000s

 

[sparkymark75]

Answering my own question about figuring out cables. To suss out which two are the TP5000s, I'm going to cut the central heating power at the CU, disconnect one of those grey cables and then work my way through them to see which TP5000s switch off when I disconnect the cables at the junction box.

 

[ericmark]

I was told don't fit a TRV to room with wall thermostat. However I could not get the room, in my case to hall, to do as wanted, there was a large radiator in the hall, with coats hung over it, and a outside door, so hall radiator set to warm up reasonable fast to reheat hall when door is opened and to dry coats, to get other rooms warm needed to set hall thermostat to around 25°C which would result in house getting too hot as summer arrived.

So I broke the rules, I fitted a TRV and a wall thermostat in the same room, the hall, I set wall thermostat to 19°C which I felt was a good summer cut off point, the TRV set to defrost, then bit by bit I turned the TRV up, took a few days, until I noted the wall thermostat turn off. At which point I left them both alone. It works, when the front door is opened it cools the TRV and wall thermostat and heating switches on, when it hits around 17.5°C then the TRV starts to restrict the water flow and the radiator starts to cool, but it will in fullness of time get hall to 19.5°C which will turn wall thermostat off.

This controls my boiler, rooms are controlled by the TRV's in each room. However at 3 am hall still at 19°C and really over night I want whole house to cool, so have a programmer which switches off central heating at around 10:30 pm and on again at 6:00 am, this can mean over night it could get very cold, so a second programmable thermostat in kitchen takes over at night, set to around 17°C allows house to cool over night, but only until the kitchen hits 17°C then boiler cuts in again.

It is not a perfect system, but programmable thermostat was in stock so cost me nothing, so whole control system was cheap, OK the eTRV in mothers bedroom and living room were a little expensive £72.99 but really the heads at £22.51 would have done the job, as I don't need to alter with my phone, but bedrooms upstairs have little more than back ground heat, standard TRV work well enough, so no point altering temperature according to time of day.

The two down stairs rooms do have varying temperatures through the day, however my thoughts of switching off and on or rather up and down as no option for off 16°C is minimum setting, simply did not work, the rooms simply took too long to cool, heating was faster, but typical set to 16°C at 9 pm and back to 20°C at 6 am the rooms never got to 16°C on a really cold night might hit 17°C heat up was a lost faster, by 8 am back to 20°C. However still two hours, and idea was to use phone so when within 10 miles from home heating would auto switch on, but for 2 hours needed around 150 miles from home, and putting it simply we rarely ever travelled that far from home.

Yes we can go into the app on the phone and change temperature, but whole idea is to be automatic, rather defeats the object if you have to access the app. So it ended up working solely on time, and these

are half the price and would do what I now do with my wifi versions. I got the Energenie MiHome as also wanted sockets with remote and fixed times etc and same hub did both.

I expect once traced you will find you have two zones, but likely it will not work as you expect with Nest as controlling just two rooms is not really going to work too well, likely you will want to control all rooms, to drop or raise the hall in my house by 2°C does not cause the other rooms to vary, OK completely off yes, but any small change is compensated by the TRV so hall may get cooler or warmer, but other rooms stay the same.