Installing Nest

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hi all

just been assessing my ageing heating and the work needed to install a more modern thermostat and heat link.

I am having trouble finding the wiring centre, see below for the setup in the airing cupboard and a pic of what it think is the wiring box -

Overview.jpg




WC.jpg


how do i go about confirming this? Also, how on earth do i make sense of that rat's nest of wires?

The other components are a Honeywell LP722 and a simple analogue wall-mounted stat in the hallway

cheers
Dan
 
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It's a home made wiring centre, and to make sense of it a suitably skilled person would have to identify what each of the wires actually does.

However, all is not lost. If you want to upgrade, the easiest path would be to get a smart stat that replaces the Honeywell LP722. Hive Dual Channel for example would be fine, Hive Dual Channel and LP722 have exactly the same connections so are a straight swap. No need to touch the wiring at the 'rats nest'. [Nest would be slightly more difficult. Its Heat link would still replace the LP722, but the connections are in a different format]

LP722
1673271798556.png


1673271822789.png


A small wiring mod would also be required to take the old analogue room thermostat out of service. Basically, its two live switching wires would need connecting together.
 
Last edited:
It's a home made wiring centre, and to make sense of it a suitably skilled person would have to identify what each of the wires actually does.

However, all is not lost. If you want to upgrade, the easiest path would be to get a smart stat that replaces the Honeywell LP722. Hive Dual Channel for example would be fine, Hive Dual Channel and LP722 have exactly the same connections so are a straight swap. No need to touch the wiring at the 'rats nest'. [Nest would be slightly more difficult. It's Heat link would still replaces the LP722, but the connections are in a different format]

LP722
View attachment 291741

View attachment 291742

A small wiring mod would also be required to take the old analogue room thermostat out of service. Basically, its two live switching wires would need connecting together.
cheers for the input - i thought it was a home made effort

with regards the Nest and wiring out the old stat, what if i want the new Nest stat to replace it, in the same location, can i just use the existing wires?

its the same as this, without the earth

1673272593197.png
 
I ripped it all out, and started again from scratch, I ended up with two wiring centres, as the Nest heat link has not got enough room inside, I used Nest as only two cores between boiler and where I wanted the thermostats, and Nest would work with two cores both supplying power and sending data, however in hind sight, and hind sight is easy, Nest was not the best option.

I would say one wait until summer, don't want to loose heating now, and two work out what you want in the end.

In the main much of what we want can be achieved with electronic TRV heads. The wall thermostat is only there to stop the boiler cycling. This is not always the case, but start by working out what you need.

If you live in an open plan house, likely one thermostat can serve the whole house, but most homes have internal doors, so each room is independent, however in the main we use the TRV's to stop over heating, and don't need them to make the boiler run, however often wind and sun can change which room is the coolest, so often we need more than one sensor to work out the homes temperature. This is where Nest falls down, as the UK version does not have temperature sensors which can be placed in other rooms, only the US version has them.

Most UK systems use a TRV head as the remote sensor, often only need one or two linked heads, the rest can be cheap non linked, I paid £15 each for my electronic heads in 2019, I would look at the Terrier i30 and the eQ-3 heads for cheap electronic.

But the expensive type, we have Hive, Wiser, EvoHome, Tado and sure there are more, who do linked heads, Hive does not support OpenTherm, Tado it seems only the EU version supports OpenTherm, most the OpenTherm is an add on module, but no point looking is the boiler is not OpenTherm.

Wiser TRV heads claim to have algorithms to work out how long it takes to heat a room, not a clue if they work. My first electronic heads were Energenie, the anti hysteresis software was really OTT, I had to cheat and set to 22 for an hour then back down to 20. Which means although the heads have geofencing, can't really use it.

The geofencing with Nest if rubbish, as it does not allow you to set the distance, all you can do is set the Eco and Comfort temperatures.

I did use existing cables, but that was it, OK mine was a real mess when I moved in, but Nest does have volt free contacts so you can get it to do anything you want. But first question is what do you want it to do?
 
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with regards the Nest and wiring out the old stat, what if i want the new Nest stat to replace it, in the same location, can i just use the existing wires?

Yes you can, but in that case, you would need to trace the cable back to the rats nest (or wherever it goes) and disconnect it completely from the 230V mains wiring. Once it is disconnected completely, it can be used to connect the Heat link T1 & T2 to the Thermostat T1 & T2. This is only a 12v connection, so the cable must not be connected to any mains wiring.

When the cable was disconnected at its origin the terminals that the yellow and red wires have been removed from need to be linked together to complete the circuit.

If you don't feel competent to do that the old thermostat can be removed, the wires put in to a junction box and the yellow and red wires joined together, and the blue wire isolated.

You would need to run another wire from the Heat link to the Nest thermostat for T1 & T2, or use a plug in power supply for it.
 
I ripped it all out, and started again from scratch, I ended up with two wiring centres, as the Nest heat link has not got enough room inside, I used Nest as only two cores between boiler and where I wanted the thermostats, and Nest would work with two cores both supplying power and sending data, however in hind sight, and hind sight is easy, Nest was not the best option.

I would say one wait until summer, don't want to loose heating now, and two work out what you want in the end.

In the main much of what we want can be achieved with electronic TRV heads. The wall thermostat is only there to stop the boiler cycling. This is not always the case, but start by working out what you need.

If you live in an open plan house, likely one thermostat can serve the whole house, but most homes have internal doors, so each room is independent, however in the main we use the TRV's to stop over heating, and don't need them to make the boiler run, however often wind and sun can change which room is the coolest, so often we need more than one sensor to work out the homes temperature. This is where Nest falls down, as the UK version does not have temperature sensors which can be placed in other rooms, only the US version has them.

Most UK systems use a TRV head as the remote sensor, often only need one or two linked heads, the rest can be cheap non linked, I paid £15 each for my electronic heads in 2019, I would look at the Terrier i30 and the eQ-3 heads for cheap electronic.

But the expensive type, we have Hive, Wiser, EvoHome, Tado and sure there are more, who do linked heads, Hive does not support OpenTherm, Tado it seems only the EU version supports OpenTherm, most the OpenTherm is an add on module, but no point looking is the boiler is not OpenTherm.

Wiser TRV heads claim to have algorithms to work out how long it takes to heat a room, not a clue if they work. My first electronic heads were Energenie, the anti hysteresis software was really OTT, I had to cheat and set to 22 for an hour then back down to 20. Which means although the heads have geofencing, can't really use it.

The geofencing with Nest if rubbish, as it does not allow you to set the distance, all you can do is set the Eco and Comfort temperatures.

I did use existing cables, but that was it, OK mine was a real mess when I moved in, but Nest does have volt free contacts so you can get it to do anything you want. But first question is what do you want it to do?
cheers for this really insightful

simply, i want greater control over the heating, the Honeywell can be programmed but its a right pain to change and it just feels old. It would be nice to have smart valves on the rads to zone the house too, i think that makes sense and would have benefits cost wise i assume?
 
It has I am sure saved me money, with my main house I have 11 radiators, the bathroom ones have mechanical TRV heads with on, other is thermo syphon, so I have 9 electronic heads, 5 being the eQ-3 and 4 being the Energenie Mihome, the idea was to connect the 4 MiHome TRV heads to Nest, however Nest has withdrawn support, so they are also now stand alone.

This guide tries to compare controls however there are clearly errors as it says Nest can use Energenie which is no longer correct.

However even with linked TRV heads, it is unlikely you will need all rooms linked, I may not use same bedroom as my wife, but do want it heating at the same time, so one TRV telling boiler to fire up is enough. That TRV on the cooler of the two rooms.

So likely I could get away with 2 linked TRV's and rest stand alone, so if you have 6 rooms, then having 4 stand alone programmable TRV now, with idea of adding two linked ones latter, seems a good interim move.

Job one measure the thread on the TRVs, 30 mm x 1.5 mm is the normal, the eQ-3 comes with kit for RA, RAV, and RAVL heads, but if not one of those, it may need the TRV base changing as well.
 
It has I am sure saved me money, with my main house I have 11 radiators, the bathroom ones have mechanical TRV heads with on, other is thermo syphon, so I have 9 electronic heads, 5 being the eQ-3 and 4 being the Energenie Mihome, the idea was to connect the 4 MiHome TRV heads to Nest, however Nest has withdrawn support, so they are also now stand alone.

This guide tries to compare controls however there are clearly errors as it says Nest can use Energenie which is no longer correct.

However even with linked TRV heads, it is unlikely you will need all rooms linked, I may not use same bedroom as my wife, but do want it heating at the same time, so one TRV telling boiler to fire up is enough. That TRV on the cooler of the two rooms.

So likely I could get away with 2 linked TRV's and rest stand alone, so if you have 6 rooms, then having 4 stand alone programmable TRV now, with idea of adding two linked ones latter, seems a good interim move.

Job one measure the thread on the TRVs, 30 mm x 1.5 mm is the normal, the eQ-3 comes with kit for RA, RAV, and RAVL heads, but if not one of those, it may need the TRV base changing as well.
If I were to add a set of valves how would these interact with my thermostat?

Would it be a case of when the thermostat reaches the trig temp the valves are active until they reach their temp or the thermostat reaches its temp? Assume the thermostat will always be the main factor?
 
I do not know what boiler you have, this does make a difference, but basic idea is the TRV showily reduces flow as room warms up, either forcing more water though the other radiators, or lifting the by-pass valve, this will then return warmer and warmer water to the boiler, if the boiler can it will then reduce output, and once it can't reduce output it will start to cycle off/on in what is called the mark/space ratio.

But what it can't do is switch the boiler completely off when warmer weather arrives, so we put a thermostat in a lower floor room, as heat raises, in a room normally kept cool, as don't want the boiler to fire up in the morning if it is likely to be a warm day, with no alternative heating, this includes the sun through windows, and no outside doors.

Don't know your house, but my house no such room. So often next best thing is the hall, but fit a TRV so it can reheat fast, but TRV closes before the thermostat is triggered, so thermostat stays always on in the winter.

But although that would work if we keep rooms heated 24/7, we don't, so now looking at speed, so the lock shield valve setting becomes important, and really better if we monitor at least two rooms, in real terms one with thermostat in, and one with a linked TRV head, of course ideal is every room with linked head,
EVO-home1.jpg
a central hub where you can control each room would be the bee's knees, but Honeywell EvoHome is not cheap, so in non main rooms,
EQ-3 Bluetooth Smart Radiator Thermostat.jpg
Using stand alone programmable heads is likely good enough, the one shown is bluetooth so if two used in same room they can be linked. Also it can connect to one phone so can control from phone when close enough, there is also the Terrier i30
terrier-i30.jpg
which does not have bluetooth option, showing picture as it shows what adaptors come with both makes, I paid £15 each for bluetooth eQ-3 in 2019 before brexit, prices now seem to have gone up.

Yes without linked TRV heads setting up the wall thermostat and the TRV can be a bit fiddly. This house my problem is hall cools too slow, mothers house it worked A1, the wall thermostat was set about 1.5°C higher than the TRV, heat raises and the wall thermostat is higher than the TRV, and on warm days the wall thermostat would switch off, on cold days the boiler would modulate (turn down) so there was hardly any hysteresis in the temperature.
Temp_variation_TPI.jpg
this picture shows what hysteresis is, and any on/off thermostat must cause some hysteresis, but with a gradually opening or closing of a TRV or with thermostats connected to the ebus (Most common is OpenTherm) we get this
Temp_variation_OpenTherm.jpg
at least that's the theory, my boiler does not modulate, it cycles instead, that's common with oil boilers, however it still works with TRV control, the wall mounted thermostat is basic there so I can turn boiler on/off without going outside and walking down the steps to under main house where the boiler is, and it also connects to mobile phone, so when away from house heating auto turns off, but most the features have been turned off, and my boiler does not support OpenTherm, very few oil boilers can modulate, only gas tends to do that.
 

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