Help replacing Honeywell T6 with meross thermostat

[psytcp]

Hi, I have the Meross thermostat which I used in my old house without problems by connecting L, N and NO.

However the new house currently has a Honeywell T6 thermostat in the corridor and a Honeywell unit in the closet upstairs (I'm assuming there used to be a tank/system boiler previously).
The current boiler is a Ideal Logic combi boiler 35

The main issue I have, and that's as far as my knowledge goes, is that there's only 2x 20v cables to the current thermostat from the honeywell unit in the closet.

However the cable itself is a 3-core & earth going behind the thermostat which might be useful.


I'm willing to repurpose the 3-core& earth going to the thermostat but I don't even understand what cables/signals does this boiler need so that it can be controlled with a thermostat.

Thanks in advance

 

[CountryFan]

I don’t know why you want to get rid of a good thermostat, for what I see as cheap Chinese crap. What you have is mains switching and the 20v is to power the thermostat instead of batteries.

So to use the Meross place instead of receiver and use the same wires:

L to L
N to N
A to Common ensuring link is maintained
B to NO
Park and sleeve the cpc/earth

Test the boiler for safe functioning as you have removed the cover which forms part of the combustion circuit

 

[RandomGrinch]

However the cable itself is a 3-core & earth going behind the thermostat which might be useful.

Yes, the 3 core and earth should be reusable to power the Meross in the existing thermostats location.

However, to work out the wiring correctly, we could do with knowing where the grey and black wires to the thermostat/timer terminals on the boiler, turn into the red and yellow wires on the Honeywell unit.
The wires can sometimes be joined behind the FCU, or in a small wiring centre etc.

 

[ericmark]

I can see the point in improving, the control, but @Stuckinarut says the old thermostat is a better than the one you want to replace it with, although not really wired up to take advantage of its superior features.

Looking at this

it seems the problem is the old thermostat is in two sections, and the new one is a single device. But somewhere

yellow and red become

black and grey, and I have no idea where or why. I can have a guess, that somewhere there is a motorised valve, or at least a junction box.

What I don't understand is why when the boiler and existing thermostat have OpenTherm why it is not used. My guess was the thermostat was fitted with a previous boiler, and the installers of the new boiler took the easy way out, with simple on/off switching.

I can see the temptation of using a thermostat you already have, but clearly you need to do some investigation work, and also need to consider if using the thermostat from the old house is really worth it.

The problem is, heating may work, but does it work in an economical way? And to be frank, not sure how much it would save, a poor control may be 75% efficient and a good one 90% efficient, so only 15% difference. But if you include only heating rooms which are used, that will increase, but every home is different. So for me in a home with 14 heated areas, only heating 4 to 20ºC for living room, and 17ºC for kitchen and bedrooms will save me a fortune, but my son, with two children, there is not really any part of the home which does not need to be below 19ºC so his options much reduced compared with me.

So I have 9 electronic TRV heads, all his heads are mechanical, I use two thermostats to trigger the boiler, he only needs one, as an open-plan house.

I made a mistake, I brought in my case 4 x Energenie TRV electronic heads which were claimed to work with Nest, OK I did not know that was not the case, and once I had Nest Gen 3 I was determining I was going to make it work, but in the end I admitted defeat and installed Drayton Wiser, wish I had done it two years earlier.

Think about it a little first, is it worth trying to use the old thermostat from the old home, or is this the time to install a better system.

 

[psytcp]

Thank you very much for all your answers. I've now successfully installed the new thermostat with the suggestions from @Stuckinarut.
So the B cable from the old honeywell box went to the NO on the meross as suggested, while the A was completely left out as it seems to be a spare Live from somewhere else (completely on it's own via another 3 core cable-and was not bridged to L as honeywell diagram suggested).

I understand that honeywell has better hardware components than meross so no argument here and this is definitely not money related swap as I had the more expensive thermostat already in hand. However when it comes to software (in a smart home era this is important) it seems that honeywell are stuck in the 2000s. For example the heating usage updates 2 days later and the scheduling is inferior compared to meross, even the accuracy of the temperature sensor is far off on honeywell. We can say that this is just a matter of what suits best the needs of every household and there's no one-fits-all solution. Thanks again!