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Sorry it's another nest heatlink problem.

Discussion in 'Plumbing and Central Heating' started by GothicGeisha, 6 Sep 2019.

  1. GothicGeisha

    GothicGeisha

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    20190908_225234.jpg 20190908_225239.jpg

    ****Update****
    I have managed to wire it back up, no trips etc, as can be seen by the 2 new pics above. But still no heating, asked a local heating engineer after showing him the pics as no one replied on here & he said "I think that black (now identified as RT) goes to the T2 port coz that the way it looks in the pics"..... ‍♀️) clearly doesn't otherwise I'd have heat.


    Turned off & isolated, opened the electrics box in the boiler, no RT link for me to remove, so stumped ‍♀️ but black is RT & Grey is Neutral. (Added pic of inside boiler unit)

    Only way I can warm the house is to hold in what I call the "Tophat & Ladder" buttons to run what seems a heating flush/purge & gets the boiler to run to 70°c

    Boiler shows S.30, install manual says "outside thermostat blocking heat"


    ***************
    I have followed the wiring instructions & only got hotwater, thermostat kept saying it would be 45mins till the radiators would be hot, but boiler never fired at all, run hot tap & it fired instantly. App showed everything was ok after running the checks.

    So unwired & tried again. Then after trying another way from the other threads I get nothing but a blown 3amp fuse.
    Last pic shows the way I had it going off all the other thread suggestions on here & without the black & grey wires in any connection.

    So I have removed everything, only thing that's back ok n the wall is the old thermostat.

    Issue is the wires in the 4core flex from the boiler. I have identified the mains L, N & E wire, red & yellow thermostat ones, L & E ones in the 4core & where they go, but dont understand where to put the Black & Grey ones from the 4 core as the grey was in N wire & the black looked like it went to the earth originally & I dont want to open the boiler if possible(read the screaming replies "dont do it " lol), but they dont work when wired there the first time.

    So I'm thinking they go to 4 & 6?
    Just haven't tried that yet as it was late & very dark when I was fiddling, so I just unwired & isolated the mains by blocking & removing the fuse. (I'm based in the UK, assume its S plan as theres no gravity system anymore & dont have aircons)

    If it's the plan were I have to remove an internal link, then I will look into it more, before opening the boiler. But I've seen the boiler cover off for a service & know the wiring system is at the bottom in a flip out box.

    And yes the wires are really short in some places & I've had to extend with blocks as theres no other junction box, that's another thing I'm looking into once I know it works as then I will be able to label correctly. But that's what happens when the boiler company installers cut out the original Randall rather then unscrew it.

    • New- Nest 3rd Gen + Heatlink
    • Old- Danfoss 130 (randall) programmer
    • Old- Seimens thermostat
    • Boiler- Vaillant EcoTec Pro28

    TiA for any help.
     

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    Last edited: 9 Sep 2019
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  3. stem

    stem

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    That's a real mess, and probably why no one has replied. It would appear that a new boiler has been fitted to an old installation and the existing wiring and controls mashed up to it. I suspect that you have a combi boiler, but as the EcoTec Pro28 comes in several versions, so I can't say for certain. If it is a combi and you don't have stored hot water now (ie a hot water cylinder) then the existing wiring, timeswitch and thermostat should be taken out and the Nest Heat link wired directly to the boiler as if it were a new installation. With some boilers, it is necessary to open up a room sealed compartment to access the boiler wiring terminals, and if this is the case with yours, it is a job for a registered gas installer as they will need to perform checks to make sure it is properly sealed up again afterwards.

    On the other hand, if you still have a stored hot water system, the design of the existing plumbing which you don't tell us anything about, might be too old to work with the functions provided by the Nest.
     
  4. ericmark

    ericmark

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    I found the Nest terminals are only just big enough for one wire, so I put a wiring centre under it New_wiring_centre_etc.jpg that means I have the ability to have one line feeding three terminals in the heat link without need for two wires in any terminal, I will not claim it is neat, upper_wiring_centre_plus_heatlink.jpg but at least I can trace each wire. I also took the time to plan out what would go where, C_Plan_My_HouseS.jpg yes it took some time to plan it out, but once done wiring was easy. There are too many wires for most people to work it out in their head without writing it down. I also had problems but it was the software set up, not the hard wiring. Nest can be configured to work with nearly any boiler, but you have to sit there and plan it out first.
     
  5. GothicGeisha

    GothicGeisha

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    It is a mess Stem, I took all the plates off and was like "WTF?" I couldnt get over how many wires were squeezed into each terminal. And it seems that the boilers power supply is run from the programmer and not the other way round. Damn council for you lol, all the wires are too short etc, you can see where it looks like the just cut the old programmer out, they've just put a blank plate over the top of the old power socket near the ceiling after fitting the new boiler, I asked if I could remove that & plaster the wall & the reply was "I wouldn't as it might still be live" that was a Vaillant engineer too.

    So it looks like I will have to get a junction box & have it fitted that way. As it's just caused a headache so far & none of the wires seem to stay in the nest terminal no matter how tight.

    It is a combi now, the system I had was a gravity with separate water tank & I must say I'm young, but old fashioned, I want my cylinder back, I hate this waiting for hot water to run & if I set the boiler to Comfort so I get near instant hot water, it chews through my gas credit.
    The boiler & these 2 way controls that they've fitted to the opposite sides of the original rad controls makes the livingroom & bathroom roasting even tho there controls are low, the hallway where the thermostat is in the wall not hot enough to trigger that off yet all the rooms upstairs & kitchen seem colder. I can't find the correct balance with it at all & during winter I'm up & down fiddling with the thermostat on the wall trying to get it to either switch so it triggers for heat or knock off due to it being too hot in 1 room.
    That's why I wanted one I could adjust via my phone.

    I hate this new system
     
  6. GothicGeisha

    GothicGeisha

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    Ericmark, this is what I'm going to have to do, it's on my shopping list for today, then I'll be hunting for a decent priced sparky to sort it, unless nest pros are reasonable?
     
  7. stem

    stem

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    As it's a combi, and assuming that it already has a suitably installed mains electrical supply, if you were to use a 'plug in' 12v power supply for the thermostat, then just one short single cable from the boiler to the Nest Heat link is all that is needed, so won't take very long for a suitably skilled person to install.

    Nest 1.JPG

    If you prefer to power the Nest Thermostat from the Heat link, instead of using a separate 12v power supply for it, then another cable between the Heat Link and thermostat is required, which will take longer depending upon what's involved in running the cable. However, you may find that the installer may agree for you to run the cable before they come to connect it up.

    Nest 2.JPG


    Ask someone to sort out the existing rats nest and they will be there all day.........
     
    Last edited: 10 Sep 2019
  8. ericmark

    ericmark

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    If it were my house, I would chisel out wall at the side of the switch by the heat link and fit a double socket box with a length of terminal strip, so all wires can be terminated into that terminal strip. Either on the blanking plate or above the new socket box fit the Nest I think likely above it. Then only one wire in each terminal in the Nest heat link.

    However that does not cure the problem of rooms too hot, I bought TRV head's from here [​IMG] to ensure rooms do not get too hot, [​IMG] shown second is the Energenie TRV head which pairs with Nest I have used the Energenie heads for three years, and I can say they do work well, the cheaper one not done a winter with, so can't say how well they work. But clearly huge difference between £15 each and £40 each.

    I found the Energenie highlighted a problem which could have been likely cured without them if I had realised what the problem was, in the old house many of the TRV heads are on the return, the valve will work either way, but being on the return radiator gets hot before the return gets hot so by time the valve is closing the radiator is really hot, result is it over shoots. Once I had the Energenie head fitted which has two sensors one air and one water the latter compensates for air being warmer when radiator is on, then I could see both target and current temperature in °C not silly *123456 so I could see the room was over shooting, so I simply closed the lock shield valve bit by bit over a few weeks until the target and current temperatures matched most of the time.

    Once done then the rooms followed the programmed temperatures well, within 0.5°C most of the time. So had I then replaced the Energenie with standard head it would have likely also worked. The cheaper electronic head you only see target temperature it does not show current, so you would need a separate thermostat so not as easy as with more expensive version.

    However the cheap version can be set on the actual unit and it does not require a hub, and has other features like open window shut off, so I use one in kitchen so when we unload food from car the radiator turns off while back door wide open.

    If you don't want the Bluetooth the same TRV head is sold for £10 each, (screwfix £20) I prefer not to bend down to read and set so got Bluetooth version.

    So it would seem you did not need Nest to cure problem, electronic TRV heads would have fixed it?

    Modern boilers need the return water to be under set temperature to gain the latent heat from flue gases, to do this they modulate i.e. turn down flame height, there is two ways to control modulation, one return water, the other connection to the ebus that is what the OT1 and OT2 is for in the heat link OT = Opentherm. The boiler has algorithms which control modulation and switching the boiler off/on can upset them, however if using the return water temperature for control then there reaches a stage where the boiler can't modulate any more and it cycles and unless some thing stops it, it would continue to cycle all summer. So the traditional idea is a thermostat in the coolest down stairs room with no outside doors or alternative heating.

    Don't know your house, but in my house no such room, so closest is the hall, but clearly it has an outside door, because Nest and Energenie TRV heads can be linked, having a TRV in the same room as Nest works well, so the room (Hall) reheats fast, until nearly to temperature then slows down allowing rest of house to also heat up.

    Other makes use different methods, EvoHome reads the temperature of rooms from the TRV head, Hive uses heat on demand and the TRV head switches on the thermostat, but all have some connection between wall thermostat and TRV head. And we today need programmable TRV heads to save heating costs, and to ensure all rooms at required temperature, the heating is central but control is room by room.

    Some houses are designed in a way where a single wall thermostat will work, I have lived in an open plan house, but most houses have doors on there rooms so need the TRV to control each room.
     
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