Replacing a Drayton CombiStat Thermostat to Meross MTS200B WiFi Thermostat

[MFD]

Hi,

Need a little guidance, trying to replace my analogue Drayton CombiStat to a Meross MTS200B, however I can’t get it to work, fires the boiler up then cuts off and cycles on and off.

This is how I’ve wired it;

N (neutral) wire to Terminal 1 on MTS200B;

L (live) wire to Terminal 2;

Switched live (grey wire) to Terminal 3.

And used the bridging wire to connect terminals 2 and 5 on the MTS200B.

 

[CBW]

Wiring I think appears ok, however check the live is in fully. Apart from that, double check the heating temperature on the front of the boiler.

 

[ericmark]

The old thermostat should have a neutral, but does not need a neutral.

However since boiler fires up, I would assume either a motorised valve is closed, or a pump is not running.

 

[CBW]

The old thermostat should have a neutral, but does not need a neutral.

However since boiler fires up, I would assume either a motorised valve is closed, or a pump is not running.

Combi boiler and no mention of dual zones.

 

[RandomGrinch]

And usually we would advise turning the timer to continuous - I'm not sure how to do that in this case?

Set a programme with a start time of 00:00 and an end time of 23:59?

Although I don't think that would cause the cycling symptoms?

For reliable operation, it may be worth finding a way to bypass the clock anyway.

 

[ericmark]

What does meter read when measuring between line and neutral? Let's ensure at least you have power when running to thermostat.

 

[RandomGrinch]

What does meter read when measuring between line and neutral? Let's ensure at least you have power when running to thermostat.

Shall we make some assumptions?
The wiring is neat, using grey, black and brown, 3 core and earth. The black wire has been oversleeved blue and the grey oversleeved brown.
The previous thermostat was working correctly, and the stated problem is that the boiler fires up and then cycles, NOT that the thermostat isn't turning on.

I don't know about you, but that strongly suggests to me, that there is at least power running to the thermostat!

 

[ericmark]

I don't know about you, but that strongly suggests to me, that there is at least power running to the thermostat!

My thought was maybe power when not running but what was thought to be neutral is not, and once the boiler runs the thermostat loses power. But to measure does not harm, so measure, no one would attempt to swap a thermostat without some sort of meter to prove dead.

 

[MFD]

Hey all, just wanted to say thanks for the input.

I’ve tried all the suggestions and also reached out to Meross customer support, but unfortunately it was a swing and a miss.

The closest I got to it working was to swap the wire NO to NC on MTS200B, this fired up the BIASI boiler, however the thermostat itself still wouldn’t stay on.

So I’ll think I’ll be returning it and sticking with my analog thermostat.

Cheers

 

[CBW]

Could have been a faulty thermostat