Another Meross MTS200 Thermostat wiring help I'm afraid

[BritishDragon]

I've read through a few past threads regarding wiring a Meross MTS200 but their wires are different to mine so could use some help please.

I am replacing a Honeywell CM907(A) with the Meross. It had only 2 wires (Black and Red) connecting to the Honeywell (I assume Live & Neutral but tbh I don't really have a clue). I think that there's also a green & yellow wire that is connected to a screw on the cavity pattress box (is this an Earth wire?).

I connected the 2 wires to L and N on the new Meross thermostat. (Black to port 1 (N), Red to port 2 (L)). The thermostat has power, and I connected it to the router and phone app without issue. When I turn up the temp setting on the display or via the app, it does click as though the boiler should then fire up and heat the rads, but other than the 'click' nothing happens.

Upstream from the thermostat, I have a Honeywell Heating & Hot water timer control unit. I have set the heating to Continuous on that and wanted to control schedules via the Meross instead.



Pic 1 is old Honeywell thermostat - Someone else disconnected the Red & Black wires so I don't know which ports these were connected to unfortunately
Pic 2 shows a small connector wire that came with the Meross but there is no information what to do with it. Does it need to connect L with COM or similar?
Pic 3 shows the 2 wires in the Meross unit
Pic 4 shows the yellow/green wire
Pic 5 shows the Honeywell Heating/Hot Water timer control next to the boiler
Pic 6 is the Meross booklet

 

[ericmark]

It is very unlikely that a thermostat with two wired connected is line and neutral, far more likely line in and line out.

So you need a neutral, but not any neutral but a neutral from the same circuit as the lines.

The standard instructions for central heating is all supplies should come from the same circuit.

There are a number of reasons, in my case the central heating is battery backed, but also borrowed neutrals are dangerous.

So with a thermostat and base, often the base can be with the motorised valves or boiler, only the thermostat needs to be placed in the location to be monitored.

As far as I am aware only Nest e has a battery powered base, all others need 230 volt to the base.

There are all in one options which are battery powered, but in most cases if you have only two wires then modern thermostat needs to be battery powered.

 

[CBW]

If you read the instructions it mentions Com and NO, which you have nothing connected to. As above you have a Live and switched live (N) on the Honeywell, but load side.

 

[BritishDragon]

Thanks for your replies. Apologies, I'm unsure what you mean by the sentence
"you have a Live and switched live (N) on the Honeywell, but load side."

Is it looking like the Meross thermostat is a non- starter with my particular wiring?

Thanks

 

[CBW]

Thanks for your replies. Apologies, I'm unsure what you mean by the sentence
"you have a Live and switched live (N) on the Honeywell, but load side."

Is it looking like the Meross thermostat is a non- starter with my particular wiring?

Thanks

Apologies, I didn’t mean to cause confusion. Basically the wires are Live and switched live. On the Honeywell diagram it states it’s N, but it’s the load side (switched live). You are correct, it’s a non-starter.

 

[RandomGrinch]

On the Honeywell diagram it states it’s N, but it’s the load side (switched live).

Sorry for being a bit pedantic - the Honeywell diagram has confused many.
The rectangle in the diagram represents the load in the circuit (In this case the boiler - the symbol could also be interpreted as the symbol for a resistor; which would still be relevant, as most connected loads would be resistive!).
So the diagram doesn't state that terminal B is connected to N(eutral) it is simply showing schematically, that N connects into one side of the load and the switched live from terminal B connects into the other; completing the circuit.

 

[CBW]

Sorry for being a bit pedantic - the Honeywell diagram has confused many.
The rectangle in the diagram represents the load in the circuit (In this case the boiler - the symbol could also be interpreted as the symbol for a resistor; which would still be relevant, as most connected loads would be resistive!).
So the diagram doesn't state that terminal B is connected to N(eutral) it is simply showing that N connects into one side of the load and the switched live from terminal B connects into the other; completing the circuit.

Thanks, I knew my explanation wasn’t spot on.

 

[BritishDragon]

Thanks for all of the help provided. I have returned the Meross and now believe the Tado Smart thermostat V3+ is suitable after reading this thread:

Honeywell CMT907A to Tado Smart thermostat

Hi, I'm trying to figure out the easiest way to fit a smart thermostat. I currently have a honeywell cmt907a backplate with cm907 thermostat on top which has two wires going into it... If I've looked at it right (photo attached). A: live B: switched live Other wires available are a blue...

www.diynot.com

It takes batteries for power and from my reading I believe that my red wire (live) will go to COM and the black wire (switched live) will go to NO