Meross MTS200 Install

[GavinT79]

Hi all, I have been through the other posts on this but they don't appear to be resolving for me. I have purchased the Meross MTS200 thermostat and connected, but it does not switch the heating off. The boiler remains on constant, supplying heat. Does anyone have a thought as to why this may not be switching off?

This is my old thermostat with a wiring diagram.

Showing it connected and this works as expected.

And the Meross effort.
I have tested this with and without the bridge from com
Any thoughts would be helpful! Cheers....

 

[EFLImpudence]

Does the boiler go off if you remove the black wire from NO?

 

[GavinT79]

Thanks for getting back! If I remove the black wire from NO, the thermostat no longer powers up.

 

[EFLImpudence]

If I remove the black wire from NO, the thermostat no longer powers up.

Do you mean the boiler no longer powers up?

 

[GavinT79]

No sorry, the thermostat. The display screen is blank.

 

[EFLImpudence]

Ok. That doesn't seem right.

Perhaps @stem will be along soon and offer some advice.

 

[Stuckinarut]

I wonder if Live and Switched are the wrong way around. Try black wire in L and brown in NO.

 

[GavinT79]

Sorry @EFLImpudence my mistake. There is power to the thermostat with just L & N connected. I did not connect N correctly when testing. Been back and forth with this a lot so missed that. The heating is still constantly on with just L & N connected. Cheers!

 

[EFLImpudence]

Ok. Let me recap:

You say the boiler does not stop when the new thermostat should be turning it off.
When in that state (stat not calling for heat but boiler still running), what happens when you disconnect the black wire from the thermostat
Surely the boiler must then stop.

If the boiler does stop when that is done then the new thermostat must be faulty.

If the boiler keeps running then something very strange is happening.

 

[GavinT79]

@EFLImpudence Yes that's correct.
The boiler does not stop when the new thermostat should be turning it off.
When I remove the black wire from NO (No bridge) The boiler stays on
When I test with then remove the bridge (COM & L) and remove NO the boiler stays on.
So the boiler will stay on with just L & N. The thermostat with display OFF in text via the digital display.
For sanity's sake, I wired the old thermostat back up and works as expected. Turn the temp down, boiler off.

 

[Harry Bloomfield]

You seem to be without any sensor connected to pins 6 and 7. It suggests the component needed is a thermistor, specced to be 10K Ohm at 25C.

 

[Stuckinarut]

I wonder if Live and Switched are the wrong way around. Try black wire in L and brown in NO.

Also, what boiler do you have?

 

[GavinT79]

Thanks, I have tested this with and without seeing the same outcome. My understanding is that it is optional though.

From the Meross site:
you can use the internal sensor to control the temperature and the external sensor to do the floor overheating protection(optional)

 

[GavinT79]

This is the boiler.

I also traced the wires to the main heating control

19 & 20 run to the mail control (along with L & N)

19 is the blue ( this leads to the thermostat, connected to the black wire wired to the thermostat .)
20 is the brown to black.

 

[EFLImpudence]

19 is the blue ( this leads to the thermostat, connected to the black wire wired to the thermostat .)

Is it? It looks to be connected to the grey -
and where is the brown that connects to the thermostat?

20 is the brown to black.

Do you have two blacks?


Anyway none of this explains why the boiler works with one thermostat and not the other.
All both of the thermostats do is connect the brown and black for heat.