No HW OFF Y Plan

[abrob1]

Hi all,

I currently have a Y plan heating system that previously had a Hive dual channel system installed.

I had Nest installed recently but it has been giving me problems so I wanted to revert back and as the old wiring was there, I thought it might be straight forward.

The Hive receiver was previously in the kitchen next to the boiler replacing the old thermostat control panel.

The Nest has been wired in the airing cupboard directly into the control center.

I’ve had a look at the old wiring near the boiler which was blanked off, and it seems there is only two spare wires, a yellow and blue wire (I know they can be used for anything in heating systems) bar the live and neutral, I’m thinking these were CH ON and HW ON but I’m confused as there is no HW OFF here?

The Hive was installed by a British Gas engineer and all was working fine.

How could this have been setup?

I can also see the other cables and there is a boiler 5 core wire, a 5 core wire going to the control box upstairs and then a 3 core wire from the FCU and then another 3 core from there to the contol box so I can’t see where the HW OFF would have come from.

The Nest HW satisfied has been wired to the control center to the cylinder stat and 3 way valve satisfied.

I also can’t see any loops in the control center so I’m at a loss.

I’ve wired it back in the airing cupboard with the HW OFF but I’d like to put it back in the original place near the boiler as I’ll need to replace a couple of tiles to make good of the area and blank the existing wiring off.

I also removed the HW OFF after rewiring the hive to see the outcome in case there was something else funky going on but the heating stopped working as expected.

One last thing, there is no loop between CH ON and the 3 way valve as the old room stat was disconnected so I’m not sure if this has any bearing.

Any advice appreciated.

Thanks!

 

[CBW]

Seems a strange one. The Hive was definitely in the kitchen? - that said, would still need a hot water off.

Terminal 7 in the wiring center is usually hot water off (white wire) which currently looks like it goes to the back plate, which is in the cylinder cupboard? If that’s the case, then it appears to be wired incorrectly, as that is heating on? Also a cpc/earth has been used, which isn’t good practice

 

[abrob1]

Seems a strange one. The Hive was definitely in the kitchen? Terminal 7 in the wiring center is usually hot water off (white wire) which currently looks like it goes to the back plate, which is in the cylinder cupboard? If that’s the case, then it appears to be wired incorrectly, as that is heating on?

Yes it was definitely in the kitchen which is why I’m baffled. I’ve already tried removing the HW off but then the heating doesn’t work.

From the Hive diagram (and Nest) this does look like how it’s supposed to be wired?

I just don’t understand how it worked before without the HW OFF, unless the BG engineer put a link somewhere which allowed it to bypass somehow?

 

[CBW]

What I don’t understand is why is there x2 black wires in the cylinder thermostat, unless it was this that controlled the hot water off? Perhaps one of the more experienced can assist?

 

[CBW]

@ianmcd or @stem - are you able to shed any light on this one?

 

[ericmark]

The mid position three port valve needs power to the grey wire to turn off domestic hot water (DHW) when the central heating is running. However the DHW can't get any warmer than the central heating water, so if missing it just means the valve will not travel all the way over switching off the DHW, so most people would not even realise the wire is missing.

With the modern gas modulating boiler it is important that the grey is powered, as the boiler can fail to give full output if the return water is too hot, with older boilers or oil boilers which don't modulate it would not matter.

The modern gas modulating boiler is in the main controlled by the TRV heads, the wall thermostat is just to turn off the boiler in summer months, unless connected to the e-bus, Hive does connect to the TRV heads and acts as a hub, as long as the room it is in does not exceed 22ºC, but it does not connect to the e-bus, Nest can connect to e-bus using OpenTherm, but will not connect to the TRV heads, so neither are very good systems, I have Nest Gen 3, and the algorithms are too complex, and I had to turn off most of the features, the USA model has remote sensors, but these have not been released for the UK.

However to replace a thermostat using OpenTherm with one using simple on/off likely some links will be needed in the boiler. I fail to understand why a Hive would be replaced to Nest unless using the OpenTherm option, as it would otherwise be a down grade.

I know that EPH thermostats can be set to master/slave and have both the on/off wiring to motorised valve/s, and OpenTherm, but not seen it done with Nest. The heat link has power, and two sets of change over contacts, a 12 volt supply if required for thermostat and the OpenTherm seem to remember marked OT1 and OT2, so question one are if the OT1 and OT2 terminals are used or not.

I have tried to work out wiring from pictures, but I can't identify which wire is which, with the three port valve it is easy to be miss lead by back feeds, you can see the resistors and diodes there, which make live testing hard. I will admit I have only once needed to work with the three port valve, and found the fault was a stuck micro switch in the valve.

So it may well be there is nothing wrong with Nest to start with, I would suggest to say why you want to change from Nest, as if due to faulty wiring or motorised valve you could end up going around in circles.

 

[stem]

@ianmcd or @stem - are you able to shed any light on this one?

If the cable circled below...........

.....is the same one that goes to the HTS3 cylinder thermostat here.

Then the blue wire in this cable is the 'HW Off' (aka Satisfied)

If on the other hand, this is the cable from the cylinder thermostat, then what is connected to its blue wire? I can't see from the photo.

To be honest with this installation, I would probably disconnect everything and start again from scratch but still using the existing cables. It's difficult to see the wires properly and to know where they terminate from photos.

As an alternative you could put the wiring back as it was with the Nest and put the Hive receiver in the same place as the Nest, so it would just be a matter of swapping the wires over from the Nest to the Hive. However, that doesn't take into account...

I had Nest installed recently but it has been giving me problems

You don't specify the "problems" but if they relate to a wring problem I would be inclined to get back the person who recently installed it to rectify matters. Otherwise we could be looking at wires that we assume are in the correct place but in reality are not.

 

[abrob1]

If the cable circled below...........

View attachment 312540

.....is the same one that goes to the HTS3 cylinder thermostat here.

View attachment 312542

Then the blue wire in this cable is the 'HW Off' (aka Satisfied)



View attachment 312541

If on the other hand, this is the cable from the cylinder thermostat, then what is connected to its blue wire? I can't see from the photo.

View attachment 312547

To be honest with this installation, I would probably disconnect everything and start again from scratch but still using the existing cables. It's difficult to see the wires properly and to know where they terminate from photos.

As an alternative you could put the wiring back as it was with the Nest and put the Hive receiver in the same place as the Nest, so it would just be a matter of swapping the wires over from the Nest to the Hive. However, that doesn't take into account...



You don't specify the "problems" but if they relate to a wring problem I would be inclined to get back the person who recently installed it to rectify matters. Otherwise we could be looking at wires that we assume are in the correct place but in reality are not.

Hi Stem, thanks for your advice.

The cable you highlighted is one of the boiler cables either SL or PL, there’s two black cables coming from the boiler which are then going into the connector blocks independantly and then into the wiring center.

I think disconnecting everything would be a good idea but again I’d still be left with one wire short in the wall for HW OFF.

I had an idea which might be correvt, the boiler has the two black wires as mentioned above, could these have previously been connected to the same block? And then at the wiring center, connecting to the two current blocks? If so, this would free up a cable which could then be used for HW OFF.

Are the any implications of it being done this way or have you ever seen this done? This would mean if the boiler was triggered so would the pump and vice versa but I guess this makes sense as they both need each other anyway?

The boiler I have is a Potterton Suprema 50L if this helps.

Thanks again

 

[abrob1]

Hi Stem, thanks for your advice.

The cable you highlighted is one of the boiler cables either SL or PL, there’s two black cables coming from the boiler which are then going into the connector blocks independantly and then into the wiring center.

I think disconnecting everything would be a good idea but again I’d still be left with one wire short in the wall for HW OFF.

I had an idea which might be correvt, the boiler has the two black wires as mentioned above, could these have previously been connected to the same block? And then at the wiring center, connecting to the two current blocks? If so, this would free up a cable which could then be used for HW OFF.

Are the any implications of it being done this way or have you ever seen this done? This would mean if the boiler was triggered so would the pump and vice versa but I guess this makes sense as they both need each other anyway?

The boiler I have is a Potterton Suprema 50L if this helps.

Thanks again

The main issue I have is the Nest thermostat randomly disconnects with the receiver, I’m not sure why and I’ve tried many things to try and resolve it but to no avail. One other gripe is that there isn’t a heating boost option in the Nest which I overlooked and Hive allows us to do this.

 

[ericmark]

The main issue I have is the Nest thermostat randomly disconnects with the receiver, I’m not sure why and I’ve tried many things to try and resolve it but to no avail. One other gripe is that there isn’t a heating boost option in the Nest which I overlooked and Hive allows us to do this.

I am sure there is a central button on the Nest Gen 3 base unit that my boiler service man presses to test boiler when doing the service, so there is a boost button.

My thermostat is hard wired to the base unit, and never lost connection. It has many other faults, like the thermostat falling off the wall, and going into away mode when the local EE mast was damaged by a storm, so it thought I was not home, had to switch off geofencing.

It is supposed to learn your daily routine, which may work if all doors are kept in the same position, be it closed or open, however we found likely due to kitchen door some times open and some times closed, it came up with a crazy routine, so had to also turn that off.

I did in mothers house have a wireless thermostat, which did loose the wireless connection, and did not seem to turn off when it did, the other one did fail safe, i.e. off. However with the TRV set correctly even if it does get stuck on, the room can't over heat. My TRV does have a boost button but the whole idea of the wall thermostat is to stop the central heating running during a warm day.

I have looked at the boiler manual and it seems it is a non modulating boiler, same as the oil boiler I have, in theroy the TRV should still control all rooms, but I have found the times work well but they open when boiler is not running so open more and more, then when the boiler fires up, rooms tend to over shoot, seems these modern thermostat are not designed for simple on/off boilers.

The old thermostat was designed for on/off boilers, it used a mark/space adjustment to stop over shooting. this will mess up a modern modulating boiler, but works well with older boilers. However it did not have the programmable features of latter thermostats.

I do think the Nest Gen 3 is rather poor, and likely Hive would be better, but your question was over the lack of HW off contact. Since your boiler is not a modulating type, it does not really matter that there is no DHW off control, with a modulating boiler it can cause the boiler to reduce output, but with non modulating that is not a problem. OK you can't turn off DHW when central heating is running, but do you really need it to turn off?

 

[abrob1]

Hi all,

Thanks for the replies.

I think I have figured it out with the help of my neighbours setup as they have the same system as myself (new build estate circa 2002).

The wire missing for the HW OFF (3rd wire which I needed) was repurposed as a permanent live to the Nest in the airing cupboard.

I’m not sure why the engineer decided to do this, he had all the cables he needed next to the boiler, N, L, HW OFF, HW ON, CH ON but decided to fit it in the airing cupboard anyway!

Thanks for all the help anyways to try and figure it out!