Understanding wiring for wet underfloor heating?

HappyHippyDad said:

I have not had to do the wiring for a wet underfloor heating system before. I think I started a thread fairly recently and had some very good replies which has helped me understand heating systems in greater detail. However, I have a more specific question to this particular manifold wiring diagram (see picture).

I understand most of it, but I am unsure how to locate the 'boiler enable' terminals located on the bottom left of the wiring diagram. I'm guessing these must be located in the boiler? (its a combi, no pictures, sorry!) Are they in the boiler, and if so how do I identify them?

Second question... Where it says 'heat enable' in part of the manifold wiring centre, it says LS and LR are volt free. The cable from 'heat enable' to 'boiler enable' is therefore volt free. I initially thought this meant ELV and was just poorly worded. However, I now think it means it can take any voltage from 0 up to 230V, is that correct?

lastly, they supply 2 wiring diagrams. I have attached them both. How do I determine which one to use?

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Hi mate haven't done loads of them but they are simple once you've got the hang of it. Unless you are using their manifold to connect to your entire system which you won't be if your heating cupboard is upstairs you only need a switch live to set it off I can't see the diagram on my phone, someone will point you in the right direction but they are good. If you get any trouble pairing wireless stats ring their technical they are really good as well.

HappyHippyDad said:

I understand most of it, but I am unsure how to locate the 'boiler enable' terminals located on the bottom left of the wiring diagram. I'm guessing these must be located in the boiler? (its a combi, no pictures, sorry!) Are they in the boiler, and if so how do I identify them?

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I have UFH8 Heatmiser manifold controllers in our house, but with a Heat Pump system - I'll give my understanding, for what it's worth!
You need the manual for the boiler if the method of external control is not obvious. Boiler manual easy to find on the internet!
Usually at the mains input terminals of the boiler there are L. N, and E, and switched live LS. There may also be links (nearby?) relating to what is going to control the boiler, eg Opentherm, so a link may need to be removed or added. Manual should say what to do when using Ls.
It looks in your case that your controller 'heat enable' terminals need the L from the boiler and then return LS when the controller calls for heat. These volt free contacts are indeed for mains.

HappyHippyDad said:

lastly, they supply 2 wiring diagrams. I have attached them both. How do I determine which one to use?

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The way I see it is that the wiring diagram on the left is the one provided with the thermostat and pertains to fitting that, and the one on the right is provided with the manifold controller, and pertains to that.
Correction - just realised they are consecutive pages from the same manual. I think the first is just illustrating how to connect different thermostats/programmers, whereas the second is for the Neostat thermostat/programmer.
The Neostat Air units I have are individual programmers, and you can set on/off times and temperatures for each individual zone, whereas the more basic thermostats just control temperature.
Hopefully for the things you need to connect they show the same information!
Good luck with the installation.

robd said:

they are simple once you've got the hang of it.

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As I posted in a thread a couple of weeks or so ago, the first time I came across one of UFH wiring centres, I took it home, removed the circuit board and traced out the complete circuit diagram. When I could see exactly what did what, it did, as robd wrote, become simple.
It was an hour or two well spent.

I think, at a quick glance, you can put the switch live up to your heating cupboard in lr. Assuming your pump is down with your underfloor manifold and the motorised valve is upstairs in the cupboard. Then all you need is L, N and SL at the underfloor. The actuator heads link straight into the manifold you've pictured and link individually to the neo stats.

HappyHippyDad said:

I understand most of it, but I am unsure how to locate the 'boiler enable' terminals located on the bottom left of the wiring diagram. I'm guessing these must be located in the boiler? (its a combi, no pictures, sorry!) Are they in the boiler, and if so how do I identify them?

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It depends on the boiler, and where/how you are making the connection.

For example on a larger Worcester boiler the terminal Ls is the live supply out to external controls and terminal Lr is the switched live (live return) to the boiler.
If it is a new boiler these two terminals will have a link between them that you remove in order to connect your controls.

On an older style boiler you wouldn't have a live supply out to external controls, you'd simply have a live and switched live terminal.

Basically check the manual for the boiler in question.

HappyHippyDad said:

Second question... Where it says 'heat enable' in part of the manifold wiring centre, it says LS and LR are volt free. The cable from 'heat enable' to 'boiler enable' is therefore volt free. I initially thought this meant ELV and was just poorly worded. However, I now think it means it can take any voltage from 0 up to 230V, is that correct?

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Volt free is also known as a dry contact or as a relay output.
What it means is that the pair of terminals do not supply a voltage, they are effectively just a switch.
In reality there will be a relay on the PCB with the common and N/O terminals connected to the volt free output terminals.

You connect a permanent live and a switched live to them.

If your underfloor heating is being supplied from the same switched fused spur as the boiler then you simply link the live supply to the UFH controls to the Ls of the volt free output and the Lr becomes your switched live to the boiler.

If your UFH is supplied from a different circuit then the volt free terminals allow you to connect the L and SL of the boiler circuit without creating a dangerous interconnection between the circuits.

HappyHippyDad said:

lastly, they supply 2 wiring diagrams. I have attached them both. How do I determine which one to use

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The only difference I can see is the type of thermostat used in each one, the rest looks the same.

But I also can't find my glasses at the moment so I may have missed something

A combi boiler would normally have permanent LNE and Ls + Lr terminals.
The diagram doesn't show the permanent Live (or Neutral) to the boiler though!.
Both drawings are the same so Ls of PCB connects to Ls in boiler and Lr of PCB connects to Lr on boiler.

I really appreciate all the responses so far.
I'm going to the property tomorrow and will have a proper look at the boiler and its controls. I may well come back with another picture!

DefyG said:

A combi boiler would normally have permanent LNE and Ls + Lr terminals.
The diagram doesn't show the permanent Live (or Neutral) to the boiler though!.
Both drawings are the same so Ls of PCB connects to Ls in boiler and Lr of PCB connects to Lr on boiler.

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Thanks for that. I've only dealt with system boilers! Presumably Lsupply and Lreturn.

Avo Mk8 said:

Thanks for that. I've only dealt with system boilers! Presumably Lsupply and Lreturn.

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I think that is the logic, but it's not all manufacturers, the labelling of those terminals is arbitrary and could be anything.

I now have a picture of the boiler wiring. The boiler is a vaillant vuw 306/6-3 (H-GB) ecoFIT pure 830.

The boiler has a L,N,E and RT terminal. The RT terminal stands for room thermostat.

Do I just need the LR in the wiring centre connected to RT in the boiler? This doesn't feel right as I'm completely ignoring the LS in the wiring centre. What exactly is the role of LS and LR? I realise this would also cause the S/L in the thermostat to become live. Both the boiler and wiring centre would be fed from the same FCU. It will also be a lot neater upon completion!

edit.... I've been thinking a bit more.
I think I need (as @Avo Mk8 said) a permanent live (PL) going to LS (this can just be a link in the wiring centre from the PL, or I can take it from the L in the boiler). Then a conductor between LR in the wiring centre and RT in the boiler?

The RT terminal in the boiler is the switch return live.

HappyHippyDad said:

Do I just need the LR in the wiring centre connected to RT in the boiler?

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Yes Lr will connect to RT at the boiler, you'll need to connect Ls to a permanent live.

HappyHippyDad said:

. What exactly is the role of LS and LR?

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Ls and Lr are just the normally open contacts of a relay which is energised to call for heat from the boiler or other source of heat.
In your case you need a simple 230V switched live at the boiler so you need only to give Ls a permanent live and connect Lr to the boiler.
If your boiler had a 24V ELV control connection you would connect 24V from the boiler to Ls and the Lr would become your 24V switched live to the boiler.

HappyHippyDad said:

I realise this would also cause the S/L in the thermostat to become live.

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The room stat needs to be disconnected from the boiler switched live terminal otherwise you'll have problems and the whole system will be uncontrollable.

There needs to be a motorised valve installed onto the flow pipe to the existing heating, which it looks like there is from your last picture.
From the wiring diagrams you posted it shows that you can connect the valve and existing thermostat into the heatmiser box.

diditrain said:

The RT terminal in the boiler is the switch return live.

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You should be good linking permanent live to LS in wiring centre or take it from boiler or double up from your fcu. Your choice. If you’re unsure, just remove the plug from the boiler and do all your testing first, before reconnecting it to the boiler. At least if it goes bang, you’re not blowing the boiler pcb.