A little confused on wiring diagram for heating.

Good evening all.

I haven't wired up many heating systems.

I am a little confused as to why the following diagram does not show a neutral going to the boiler?

Also, the boiler needs a permanent live (PL) but in the diagram it has the grey conductor going to it from the under floor heating control box, not the brown (which is the PL from the fused connection unit). The grey conductors terminates into 'C' terminal in the 'heat' terminal in the UFH control box. I'm assuming this must be a PL?

Thanks in advance!

Different boiler?
as there is no neutral connection to the boiler ,so to me it looks like there is another diagram you missing, and this is only the control side of the system,
the grey and orange are the feed an switch line for the boiler
is this diagram for some sort of room stat or a control centre?

poni said:

Different boiler?
as there is no neutral connection to the boiler ,so to me it looks like there is another diagram you missing, and this is only the control side of the system,
the grey and orange are the feed an switch line for the boiler
is this diagram for some sort of room stat or a control centre?

Click to expand...

Thanks for the reply. It's the wiring diagram for the control center of an Underfloor heating system (heatmiser UH8-RF)

That's a really funny coincidence, I did one of these at a school on Saturday....with 4 wireless stats.



So the way these work is that the heat enable is just a relay.
In my case....
The under floor heating pump was a simple 3 wire connection to the controller.
I had a four core flex going to a combi boiler. This flex was basically the normal supply and a switched live to tell the boiler to fire.

So I put N and E from the 4 core in the same terminals as the main supply in.
I put an extra wire from L of the main supply in to the common of the relay on the right.

I put L from the 4 core in with the common on the relay on the right.
and the SL from the 4 core in the NO terminal.
I did it this way so there would be a max of 2 wires in a terminal.

You will probably want to set at least a 1 min delay using the DIP switch as the actuators can take a while to open.
You can test the pump, each actuator, and the heat enable using the dip switches. It's a good controller.

Feel free to fire more questions....

The photo doesn't really show it well...

Tim Howard said:

That's a really funny coincidence, I did one of these at a school on Saturday....with 4 wireless stats.

View attachment 17069

So the way these work is that the heat enable is just a relay.
In my case....
The under floor heating pump was a simple 3 wire connection to the controller.
I had a four core flex going to a combi boiler. This flex was basically the normal supply and a switched live to tell the boiler to fire.

So I put N and E from the 4 core in the same terminals as the main supply in.
I put an extra wire from L of the main supply in to the common of the relay on the right.

I put L from the 4 core in with the common on the relay on the right.
and the SL from the 4 core in the NO terminal.
I did it this way so there would be a max of 2 wires in a terminal.

You will probably want to set at least a 1 min delay using the DIP switch as the actuators can take a while to open.
You can test the pump, each actuator, and the heat enable using the dip switches. It's a good controller.

Feel free to fire more questions....

The photo doesn't really show it well...

View attachment 17071
View attachment 17072

Click to expand...

Brilliant Tim.. thankyou!
I do have a few more questions, but that has certainly helped. I'll draw out my own wiring diagram a bit later and post it up, just to double check I'm right.

So..
I've drawn it out.
It doesn't make sense to me, but I think this is because I don't know what is going on in the internal electrics of the ufh control centre.

Basically I have drawn out the pump and valve exactly as in the diagram.

I have also put a link between L (mains in) and C (heat).

How does it look?
Ps.. I've left out all the actuators.

HappyHippyDad said:

How does it look?

Click to expand...

That looks spot on.
(If it's the only heating system you may not have a zone valve for the under floor heating)

Tim Howard said:

That looks spot on.
(If it's the only heating system you may not have a zone valve for the under floor heating)

Click to expand...

Cheers Tim.
There's a radiator system as well which I'm happy with.
2 zone valves (rads and ufh).
I'm starting to quite enjoy heating systems, now I'm beginning to understand them more.
It helps that the plumber is a really nice chap, so we can talk it through.

Basic principals of heating systems are a collection of switches wired in series to operate a single zone and fire up a boiler..
with other switches in parallel if required to operate multiple zones to fire up the same boiler..

e.g.
[item A]... A permanent live to some sort of single zone or multi-zone timer clock / programmer. {to decide what time(s) you want your heating / water on.}

[item(s) 'B']... One or more switched lives from "Item A" to individual thermostat(s) to monitor the temperature of the required zone(s) / cylinder. {to confirm if the zone is below the required temperature and needs heating up}

[item(s) 'C']... One or more switched lives from "Item(s) B" to individual motorised valves, (or 3-port valve), for the relevant zone(s) / cylinder, that must drive a valve motor, to open up, to allow water flow before the boiler is fired up... Motorised valves have a dry normally open switch, that will close once the valve is opened to allow the water to flow. The switch requires a permanent live onto one side and the other side is the switched live to fire up the boiler & pump. (Typically Orange wire)..

{Note:- With a multi-zone system you must be careful not to use your Switched lives from "B" also as your permanent live to the valve switch contacts, otherwise you can get a feed from another zone back-feeding through the switch contacts to hold other valves open that should be closed.. i.e. Switch contacts and motorised valve feed must be separate!}

(You can think of motorised valves as Relays or Contactors that are controlled via a Time-clock & Thermostat, that will then send a live output to fire the boiler once they have operated.)


Underfloor heating is a little bit different because it works off much lower temperatures than the typical room radiators..
So it has its own little recirculating loop of pipe(s) supplied from a thermostatically controlled zone from the boiler, plus its own circulation pump.

So, where multiple UFH zones are in use a control centre with actuators for each zone can trigger the UFH circulation pump, which can also trigger the boiler to give a supply of thermostatically controlled water for it to supply to the relevant UFH zone.

Basically you need to consider the whole UFH system just as another radiator on the system.... but a bit more strictly controlled via the UFH control centre!

UFH control centre thermostat zones may be 230v / 24v / 12v / wireless etc.. etc.. but the final output to the boiler will generally be 230v or a dry contact for you to put a supply onto!

But at the end of the day heating control systems are just a mix of series & parallel switches, with time clocks, thermostats and correctly positioned valves to get the boiler to fire up and send the hot water where you want it!

There is one improvement, you don’t want the boiler to fire unless the UFH zone valve opens.
So I’d use the orange from the zone valve to feed Common on the heat enable relay

That way if the valve doesn’t open, the boiler won’t fire up.

that diagram looks shite. the grey and orange both start from the boiler. one must be a live out (grey) and a switch live in (orange). the boiler along with having no neutral, also doesn't have a live (which would either link to grey internally or grey /orange are a 24v switched input depending on boiler / controls)

Isn’t there a separate set of terminals in the controller forUFH valve?

kerching said:

Isn’t there a separate set of terminals in the controller forUFH valve?

Click to expand...

No, not on this one.

Tim Howard said:

There is one improvement, you don’t want the boiler to fire unless the UFH zone valve opens.
So I’d use the orange from the zone valve to feed Common on the heat enable relay

That way if the valve doesn’t open, the boiler won’t fire up.

Click to expand...

Surely heatmiser must have taken this into account though Tim? The internal electrics/relays etc of the ufh control unit would know when the thermostat calls for heat. Im assuming the live terminal in the control centre for pump and valve then becomes live, followed by the NO becoming live (calling on boiler for heat).

I might give them a ring and ask as I'd also like to know why there's no neutral for the boiler when it has to have one.

I will update!

HappyHippyDad said:

Surely heatmiser must have taken this into account though Tim? The internal electrics/relays etc of the ufh control unit would know when the thermostat calls for heat. Im assuming the live terminal in the control centre for pump and valve then becomes live, followed by the NO becoming live (calling on boiler for heat).

Click to expand...

That is all true.
What I was trying say is that If the valve fails to open one day, the NO would still become live and the boiler would fire trying to pump against a closed valve. My suggestion is below.

My understanding of the sequence is:
1 - remote radio stat calls for heat, activating whichever zones you have paired it to, which can be more than one
2 - the 3 position switch above the zone(s) determines what happens next:
left position - operates relay for that zones actuator only, could be used for a zone valve for radiators, with the zone valve's orange wire firing the boiler
mid position - operates relay for that zones actuator and heat enable. The heat enable relay is a volt-free switch, hence the need to run 230v from somewhere to C as per your diagram.
right position - operates relay for that zones actuator and heat enable and manifold pump. You probably want this position for under floor heating zones.

Additionally you can add a delay between actuator and pump / heat relays.

I believe this is what you want:



With the zone switches in the right hand position, the stat will operate a zone, open the actuator for that zone, then operate the pump relay after any delay that is set, the zone valve will open powering the pump and input to the heat relay, the heat relay will have operated so the boiler will fire.

If the creepage function is turned on to briefly run the system each day in the summer, the heat enable relay isn't operated, so it is worth having it in circuit and not just linking straight through to SL at boiler.

I hope that makes sense and I haven't added more confusion! This is my go-to controller and after the first one it's simple.

Tim Howard said:

That is all true.
What I was trying say is that If the valve fails to open one day, the NO would still become live and the boiler would fire trying to pump against a closed valve. My suggestion is below.

My understanding of the sequence is:
1 - remote radio stat calls for heat, activating whichever zones you have paired it to, which can be more than one
2 - the 3 position switch above the zone(s) determines what happens next:
left position - operates relay for that zones actuator only, could be used for a zone valve for radiators, with the zone valve's orange wire firing the boiler
mid position - operates relay for that zones actuator and heat enable. The heat enable relay is a volt-free switch, hence the need to run 230v from somewhere to C as per your diagram.
right position - operates relay for that zones actuator and heat enable and manifold pump. You probably want this position for under floor heating zones.

Additionally you can add a delay between actuator and pump / heat relays.

I believe this is what you want:

View attachment 17089

With the zone switches in the right hand position, the stat will operate a zone, open the actuator for that zone, then operate the pump relay after any delay that is set, the zone valve will open powering the pump and input to the heat relay, the heat relay will have operated so the boiler will fire.

If the creepage function is turned on to briefly run the system each day in the summer, the heat enable relay isn't operated, so it is worth having it in circuit and not just linking straight through to SL at boiler.

I hope that makes sense and I haven't added more confusion! This is my go-to controller and after the first one it's simple.

Click to expand...

Thanks for such a detailed and helpful response Tim. I'll chat it all through with the plumber.

The plumber rang me yesterday whilst he was finishing the UFH. He said... 'Steve, it's not working', my heart dropped.
Luckily, he was joking. He knew I was a little worried about it and took advantage of that fact!
It all works great, tests fine and looks neat. Very happy
Thanks again @Tim Howard

Andy™ said:

that diagram looks shite. the grey and orange both start from the boiler. one must be a live out (grey) and a switch live in (orange). the boiler along with having no neutral, also doesn't have a live (which would either link to grey internally or grey /orange are a 24v switched input depending on boiler / controls)

Click to expand...

It's a wiring diagram showing how to wire the UFH wiring centre not the boiler - as you say, different boilers have different wiring systems. This just demonstrates the use of a " volts free" system or a 230v system at the boiler. But as you say, can be a tad confusing for anyone not familiar with boiler wiring

It seems that the grey wire is being used as the permanent live (PL) in this setup, which is common practice in some systems. Ensure that the grey wire is correctly identified and marked as live. The neutral might be connected elsewhere in the system, possibly through another terminal or connection point.

FastGenerations said:

Ensure that the grey wire is correctly identified and marked as live.

Click to expand...

?? eh

Nothing additional is required as Grey is a correct colour identification for a live conductor... (re: Table 51)