How To Wire Drayton Wiser 1-Channel Smart Hub to Ideal Logic Max Combi C35 using OpenTherm

[DDew]

Last year I had a new combi boiler installed alongside the Drayton Wiser smart hub system.

This is the boiler: Ideal Logic Combi Boiler
This is the controller system: Drayton Wiser Kit 1

I didn't know at the the time that the installer could wire it NOT using the OpenTherm module. I want to know if rewiring it using the OpenTherm module is something I'm capable of so I can at least feel like I've done everything to benefit from the technology I've bought.

My experience of electrics goes as far as wiring sockets and lights. If someone could tell me what wire to put where (and perhaps why), I'd be so grateful.

Here's the guide from Drayton, which I'd follow if I knew what it meant by "Set the OpenTherm cables into..." (Which ones? Live + Neutral?)

I've attached images to show how the system is currently connected.

Thank you in advance!

 

[ianmcd]

you cant with that set up you need 4 cores

 

[DDew]

you cant with that set up you need 4 cores

That explains my confusion at least.

So if the 4th core was there, presumably it would go into the OpenTherm module, but which of the existing cables would also go into the module?

 

[ericmark]

As @ianmcd says, an installed unit needs line, neutral, and earth to power it, and then also either OpenTherm or on/off wires to send info to the boiler, over sleeving green/yellow is down to the full stop in the regulation, I would say not permitted, but down to command of the English language, but this is only questionable where you have multi multi core cables, installed devices must have an earth wire available even if not used, since 1966.

As to gains of using OpenTherm, not so sure, there must be a gain, but as to how much, not so sure. It seems it varies boiler to boiler, the whole idea is to gain the latent heat from flue gas, and every time an on/off thermostat turns off, it can reset the boiler so when it restarts it does so at full output, but the word is "can" and one would have to know the algorithms used by the boiler to be sure that is the case.

I don't, so can't say if worth the effort to wire up OpenTherm, you can click on the name of anyone replying, and then "About" and see if they boost being a GasSafe guy or not, I am not, to save you looking, @ianmcd does not say, it is optional to complete details, I see you have not bothered, but do remember anyone can answer posts, as I have done, and I am only an electrical engineer.

 

[ian1182]

Is the boiler working OK at present using the Wiser? I would have expected links to L, N, 1 & 3 on the wiser back plate. Then in addition a separate 2-core cable from the opentherm module to your boiler's OT connection. That said the Wiser installation details for opentherm are not very specific. I think you contact Drayton for advise before doing anything.

Assuming the OT module is not in use at present, how is the Wiser Hub instructing the boiler to come on for CH?

 

[harrythefurrysquid]

Is the boiler working OK at present using the Wiser? I would have expected links to L, N, 1 & 3 on the wiser back plate. Then in addition a separate 2-core cable from the opentherm module to your boiler's OT connection. That said the Wiser installation details for opentherm are not very specific. I think you contact Drayton for advise before doing anything.

Assuming the OT module is not in use at present, how is the Wiser Hub instructing the boiler to come on for CH?

I'm going to go out on a limb and say it's not working with Wiser based on that photo, unless there's a new "wireless" mode I don't know about!

Needs the L&N to power the hub (already in place) and for OP's benefit either the 1&3 terminals (relay switching) or 2-core to the Opentherm module - no need for both AFAIK. Make sure the Opentherm cable is not connected to 230V on either end, or you'll let the magic smoke out.

The 2-core Opentherm cable needs to be connected as shown on Page 32 in this Install/Service manual:

https://idealheating.com/uploads/documents/Logic-Max-Combi-Installation-Servicing-Guide-222362-1_lowres.pdf

Note the Link Wire on the 230V side of the boiler, which might have been removed if it was setup for a timer.

 

[RandomGrinch]

I would have expected links to L, N, 1 & 3 on the wiser back plate. Then in addition a separate 2-core cable from the opentherm module to your boiler's OT connection.

It's a two channel Wiser, the current wiring would work.

 

[harrythefurrysquid]

OP says it's kit 1, which is single channel and correct for a Combi.

@DDew you've just got a Setup button and a Heating button on the front, right?

 

[ian1182]

If that's a photo of the back of the Ops Wiser Hub, it's a 2-channel version as the model number is WT724. The 1-channel would be WT714. Plus the diagram below the model number shows two sets of channel connections.

When I looked at the photo I thought the "Earth" core had been taped over to isolate it, if its connected to #4 then it would work. It would be nice if the connection to #4 had some proper sleeving.

 

[DDew]

OP says it's kit 1, which is single channel and correct for a Combi.

@DDew you've just got a Setup button and a Heating button on the front, right?

Ahh damn, I made a mistake. Three buttons Setup, Hot Water, Heating. Guessing that makes it 2-channel? I was wondering if the wiring was wrong how I've nevered noticed

So sorry for wasting your time.

But basically still if I want to use OpernTherm (even if it won't be worth it) I'd still need someone to replace the cable from the boiler to the hub, correct? Which means unless someone jumps in raving about it, I probably won't bother.

 

[harrythefurrysquid]

Not sure whether you can use Opentherm with Kit 2. I would give Drayton support a call. Maybe they'd be willing to do a swap, or maybe it'll work just fine with a Combi if you plug the Opentherm interface in.

Assuming it's either supported or you've swapped to Kit 1, yes, to support Opentherm you would have to add an extra 2-wire cable. It should be very easy to do with the manual I linked above (though this is usually the point where someone pops up and says you can't access that electrical interface if you're not a Gas Safe engineer).

 

[RandomGrinch]

Not sure whether you can use Opentherm with Kit 2.

I would guess so, as the module is already attached

(though this is usually the point where someone pops up and says you can't access that electrical interface if you're not a Gas Safe engineer).

Yes, and I will mention it.
To open the electrical compartment and make the required changes to the boiler, the cover of the room-sealed unit has to be removed - this would officially require an RGI to check the appliance for safety afterwards.
I will also mention that some manufacturers manage to design electrical compartments that are accessible without opening the cover - I wonder why others can't?

 

[harrythefurrysquid]

I would guess so, as the module is already attached

You'd think so.
However Drayton says: https://schneider-electric.zendesk....014449877-How-to-connect-the-OpenTherm-Module

The Wiser system currently supports OpenTherm only in conjunction with a combi boiler and a 1 channel Wiser HubR.

So I think it does need a chat with support to find out what the deal is. Might be a software thing.

 

[ericmark]

In theory OpenTherm module should only be used with the single channel model, in practice I have read it will work with the twin channel,

it should be independent cables to the supply, one should not really mix extra low voltage and low voltage together.

But although I have seem reports that is does work with twin channel, the question is does it work correctly with twin or triple channel versions?

I have seen many central heating systems which work, but not correctly, what would be interesting would be to see the real advantage of using OpenTherm, I know my boiler is switched on by the wall thermostat and stays switched on for hours, but this is rather a useless energy history, as although boiler is switched on, it is internally cycling on/off (oil so does not modulate) with gas the return water temperature can modulate the boiler, so as long as the thermostat is not cycling the boiler, it should do some thing similar to what it does with OpenTherm.

The amount the boiler modulates may vary OpenTherm to return water temperature, but not sure by how much? However for the OpenTherm to work the master controller (Wall thermostat in your case) must connect to all the TRV heads and correlate the information, this means every TRV needs to connect to the wall thermostat, however Wiser TRV heads are expensive, so the normally method is to select key rooms, maybe living room and master bedroom, and have the TRV's in these rooms connect to the thermostat, but in other rooms use much cheaper heads like these which are still programmable, but don't connect to the main wall thermostat, I paid £15 each for mine in 2019, these will not cause the boiler to fire up, but will alter the temperature of the return water, so will cause the boiler to modulate.

So if you have all Wiser TRV heads connected to the main thermostat then maybe the cost of getting the correct wall thermostat would be worth while, but if some TRV's are not linked, then maybe better left as it is.

 

[harrythefurrysquid]

@ericmark The main difference in behaviour I observed when I turned on Opentherm was that the boiler would fire up at a lower temperature when close to the set point, and also appears to run the pump longer/instead of firing. I think this would save some energy vs. just modulating based on return temperature, though it's probably a few percent. I don't see why this wouldn't work in combination with non-Wiser TRVs as long as the TRVs are not conflicting with the thermostat - i.e. just being used to stop individual rooms overheating, with the thermostat "in charge" of the overall house temp. Same as any thermostat really, vs just running the system on a timer.

My parents recently had a modern Opentherm-capable Ideal boiler fitted and they just run it on a timer, with TRVs to regulate. They were given a thermostat, but "it's in a drawer somewhere" (!). The house was warm AF at Xmas - I hate to think how much it's costing - but hopefully the boiler was doing some modulation internally. My Dad has entered his luddite phase of life so I'm not touching that one!