S Plan Plus with Nest

[padstar]

I am looking for some help if i may. The house was re plumbed a few months ago and i am now having the electrics completed.

As part of the electrical finals i have asked the electrician to wire the central heating/Hot water system so that i can finally do away with running the boiler for a few hours a day to give me hot water to have a shower.

He is happy to do it but is a new build 1st/2nd fix guy and says the plumber normally deals with it. All he wants is a schematic for him to follow and i am good to go.

I have watched a number of videos as i like to understand what is being done and there are millions of drawings online but none seem to be quite identical to what i have which is strange as its a very common set up.

WB Greenstar System boiler (located in garage)
Megaflow cylinder (located in the loft)
Nest 3rd gen stat & heatlink
1 heating valve feeding rads upstairs
Upstairs temp controlled by Nest
1 heating valve serving UFH downstairs
Downstairs heating controlled by multiple stats connected to the UFH manifold
1 valve serving CHW controlled by nest programmer

I understand that i need an S Plan + set up.

In my head i had the heatlink and wiring center being located in the loft next to the cylinder with a link between that and the boiler.

There are spurs available at the boiler and loft locations for mains power.

Does anyone have a schematic showing the wiring that i can give him to wire to?

Any help is much appreciated.

 

[winston1]

Can you explain how you can get hot water without running the boiler? I'm sure many of us would like free hot water.

 

[ericmark]

In the main the radiator zone is part of the UFH system with something like this.

Top right you can see the heating thermostat, taken from the "UFH heatmiser UH8 instructions" the Nest Gen 3 does not really lend its self to combining with the UFH as shown here.

It is a specialist job, the heating and ventilation engineer needs to design the system. This includes the selection of manifolds and controllers. The instructions for heatmiser are not the only option, but it is not a simple S plan.

The basic for any central heating system is to allow selection by user on what areas are heated, and to allow for wind and sun to alter which areas are the coolest, and to do that it needs at least two thermostats.

The humble TRV (thermostatic radiator valve) is a thermostat, and most systems use a connection to at least one of these to allow for sun and wind changes, EvoHome, Wiser, Tado, Hive all have a system where they use the TRV head to send into to the main hub/thermostat.

In USA the Nest is not the same as here, and they have temperature sensors which tell Nest the temperature in other rooms, but this has not been released for Europe, and when Google took over Nest the arrangement to use Energenie MiHome TRV heads stopped, so they are no longer supported.

I got caught out, did not realise until I tried to make the TRV's connect to the wall thermostat that support has been removed, which has reduced the Nest wall thermostat to a bit of junk, I am crossing fingers and hoping the temperature sensors will be released in the UK, but not seen any yet.

Nest e is thermostat only, Nest Gen 3 is CH and DHW control, but with Megaflow cylinders the DHW is normally part of the central heating system, the idea is to allow multi-inputs so solar, gas, and solid fuel can all feed one heat exchanger and then the CH and DHW draw from it.

This shows general idea. But this is an engineers job to plan, not a simple plumber or electrician, and it should have been all planed out before anything was installed, you can't simply throw together such a complex system, it needs safety provisions so water does not over heat etc.

It is not a DIY job, you need to get the plans from the heating engineer who designed it.

 

[padstar]

Can you explain how you can get hot water without running the boiler? I'm sure many of us would like free hot water.

I meant to have the boiler running automatically when needed rather than me plugging it in for a few hours to heat it all up. Not free hot water - That would be impressive.

 

[padstar]

ericmark - I will go back to the guys that put the system together but i am slightly confused (for the record i am trying to understand how it works, i am not planning on doing this myself).

I thought the underfloor heating has its own heating system that takes information from each of the stats to each of the zones/rooms and opens valves on the manifold to feed hot water round the system when required.

That system is then linked to the main control hub which triggers the 3rd valve asking the boiler for hot water when called for by the UFH manifold. Is this not the case?

 

[EFLImpudence]

Yes, there should/would be additional timer, valve and thermostat on Eric's wiring diagram for Hot Water but most these days would have a combi-boiler and not need them.

 

[flameport]

There are spurs available at the boiler and loft locations for mains power.

Only one of those can be used, the whole system must be supplied from one only so it can be isolated at a single position.

The Nest part is a standard S plan.
Nest 2 channel receiver, wired to one valve & cylinder thermostat for the hot water cylinder, and another valve for the upstairs radiators.


The UFH is wired according to the instructions supplied with the UFH wiring centre and thermostats.

I thought the underfloor heating has its own heating system that takes information from each of the stats to each of the zones/rooms and opens valves on the manifold to feed hot water round the system when required.

That system is then linked to the main control hub which triggers the 3rd valve asking the boiler for hot water when called for by the UFH manifold.

That's exactly how it is.

It's a standard S plan, with the addition of a 3rd valve which is controlled from the UFH wiring centre / control box.

 

[ericmark]

Megaflow cylinder (located in the loft)

The cylinder could be simply for domestic hot water, or as a hub to feed two partly independent systems, there are many ways of doing it all.

Only one of those can be used, the whole system must be supplied from one only so it can be isolated at a single position.

This is the normal way of doing things, however having a thermostat fed from a USB supply with Nest Gen 3 is common, and unlikely the USB supply is taken from the single FCU supplying main boiler, it does not really matter if a power supply is built into a thermostat, or if independent the rules clearly need to be the same. So either the USB supply needs to be supplied from same FCU as boiler, or no other power supply needs to be supplied from same FCU either.

My boiler when I moved into the house had at least 3 FCU's feeding the central heating, and they came from two independent distribution boards. Today there is only one FCU, but 10 independent supplies, 9 of which are pairs of AA batteries.

I would agree safer when turning off one FCU turns off all, using multi-FCU is asking for errors with borrowed neutrals, and for errors to be made when proving dead, but there is no strict rule saying all supplies to central heating should come from one FCU, from a single isolation unit yes, that would be normally the main isolator on incoming supply.

I would agree the manufacturers instructions often say some thing like

but it does not define same supply, with domestic I have not seen it where there are multi-supplies, so it would always be the same supply. In the building I work in yes, there are at least 3 independent DNO supplies, but that would be unusual for domestic.

I just hope @padstar has a better system to what this house did, I could no believe what I was looking at when I moved in, electrical installation company and a central heating installation company had their stickers affixed, clearly two companies to avoid, and looking at it seems unlikely a DIY job, but to turn central heating on, needed to set the time clock in main house, to on, then go outside, down a set of steps, and into the flat under main house, and plug in the pump. It was clear it needed some rewiring.

Had it been DIY I could have understood, but clearly from labels it was done by some one claiming to be a professional, seems previous owners used a wood burning open fire.

I would guess the plumber expected the electrician to fix it, and the electrician expected the plumber to do it. I think the problem is in the land of the blind, the one eyed man is king, and in Mid Wales there is not a lot of competition for tradesmen, it more down to any port in a storm, the good ones are booked up months in advance, so the poor ones can still make a living, as people don't want to wait.

I employed a plumber, who in turn employed a so called heating engineer, who admitted he did not know how to wire up a relay, so he used a zone valve instead! Electrics did not worry me, I designed my own system, but I feel sorry for anyone who can't DIY, does not matter if builder, plumber, chippy, seems good tradesman hard to find, I had to get a guy from Shrewsbury some 30 miles away, considered getting tradesman from North Wales, to stop leak on my flat roof.

Firm I volunteer for even has people from Canada working there. And common to find one working beside a guy who has travelled 100 miles or more. Isle or man and Portsmouth for example. Until I moved here I had never considered the problems getting good tradesmen.

 

[CBW]

This is the normal way of doing things, however having a thermostat fed from a USB supply with Nest Gen 3 is common, and unlikely the USB supply is taken from the single FCU supplying main boiler, it does not really matter if a power supply is built into a thermostat, or if independent the rules clearly need to be the same. So either the USB supply needs to be supplied from same FCU as boiler, or no other power supply needs to be supplied from same FCU either.

Surely as someone competent working on the system would check if something is fed from a usb supply/plugged in to a socket outlet and could use knowledge that it’s fed from a different source. If the Nest was being fed from the heat link, then this would need to be from a single fcu source same as the heating system. I think you know what @flameport was referring to, I certainly did.

 

[ericmark]

Surely as someone competent working on the system would check if something is fed from a usb supply/plugged in to a socket outlet and could use knowledge that it’s fed from a different source. If the Nest was being fed from the heat link, then this would need to be from a single fcu source same as the heating system. I think you know what @flameport was referring to, I certainly did.

Yes agreed, but a blanket statement only one FCU is misleading. It does depend on how it is all installed, in some cases there may be more than one circuit = An assembly of electrical equipment supplied from the same origin and protected against overcurrent by the same protective device(s). remembering that many do not consider fitting a FCU as forming a new circuit, if fitted to a ring final then as the name suggests that is the final circuit, so how can a FCU form a new circuit if taken from a ring final?

 

[CBW]

remembering that many do not consider fitting a FCU as forming a new circuit, if fitted to a ring final then as the name suggests that is the final circuit, so how can a FCU form a new circuit if taken from a ring final?

True. Would it be looked at as tee-ing into the ring main and spurring off (as the name suggests), then it’s a new/additional circuit?

 

[ericmark]

English language final is the last, so ring final is the last circuit, however it does not say same circuit, it says same supply, and most homes only have one supply.

The problem is many thermostats, hubs, and programmers are not volt free. And if not volt free then it must come from the same overload device, it does not matter if the fuse is built into the boiler, or a FCU fitted onto the wall, and many boilers are designed to be controlled by low voltage or extra low voltage and have provision to take the supply for the controls from the boiler as seem here often with separate provision for low and extra low voltage.

The problem arises when zone valves are added. There was once an extra low voltage zone valve, but most today are low voltage, EPH do a special thermostat with both low and extra low voltage controls, designed to work as master or slave, so up to 10 thermostats per system. The master connects to the boiler using OpenTherm (ELV) the one zone valve, and the slaves just connect to the zone valves, with the information slave to master being wireless.

This means the slaves and zone valve works in the same way as the TRV, lets face it the TRV is a zone valve. And the same way in which a TRV can connect to a hub/thermostat to relay a demand for heat to the boiler, the zone valve and slave connects to master thermostat.

We have no worries about the TRV working on a pair of AA batteries, so what is the difference to the zone valve and thermostat also having an independent supply? Be it 3 volt or 230 volt both can be independent supplies when using wireless links.

The use of radiators with TRV control be it wireless linked or not is relativally simple, one pump by-pass and boiler combination circulate water as required. Where the problem lies is using UFH where you have two independent pumps and two independent circulation water temperatures.

The UFH water is circulated at around 30ºC where the DHW needs to be 60ºC and also the radiators are also around 60ºC, the DHW is taken care of internally in the boiler with a combi boiler, but with a system boiler some external control is required, the cooler the return water the better the boiler can extract the latent heat from the flue gases, so central heating circulating water can be well below 60ºC, if the rooms are satisfied, but not the DHW due to legionnaires, so the heating engineer has to design a system with possibly three independent water temperatures.

Fortunately controllers like the heatmiser already show can do this all for him,

I question the whole idea of UFH, on one hand we are moving to fast response and reducing the amount of water in the system so radiators can heat up and cool down quicker, so rooms only heater when required, and only just enough, with geofencing systems to turn on the heating as it is detected the prospective occupants are on their way home.

But UFH takes hours to heat up and cool down, great for an old peoples home, or as a back ground heat, where the UFH holds the room at say 12ºC and radiators boost it when rooms are occupied to say 20ºC. But without a radiator to boost the room, it means the UFH needs to be on 24/7, as the response time is so poor.

Also need to be very careful with heat from other sources like the sun, you can't have bay windows facing south as when the sun comes out they will over heat. Same goes for patio doors, and also in the kitchen heat from cooking, in the kitchen the kick space fan assisted radiators makes good sense, as it can respond fast, plus does not take up much room, and since blowing out at floor level it will heat the floor surface.

Seems odd talking about central heating on the day before we are told to expect a heat wave.

 

[snb]

A lot of waffle for what is a very basic setup consisting of 2 heating zones (1 heat zone comprising the underfloor) and a hot water zone. This should be incredibly easy for any half capable electrician. The only awkward bit to remember is to turn the hot water disinfection off on the nest or you will think there is a fault as it does an hour hot water without demand once a week or after every period of electric isolation

 

[EFLImpudence]

Nevertheless - a particular qualification - G3 - is required to work on unvented systems.
Random site - https://www.gledhill.net/master-pressure-get-g3-qualified/

So why has it been left unfinished?