Meross MTS200 Install

[CountryFan]

I wonder why there’s a link in the room stat terminal at the boiler, but the old thermostat works?

 

[EFLImpudence]

I wonder why there’s a link in the room stat terminal at the boiler, but the old thermostat works?

The old one doesn't need it -

all it does is connect L to NO; the new one connects COM to NO so COM has to be connected to L.

 

[CountryFan]

The old one doesn't need it -

all it does is connect L to NO; the new one connects COM to NO so COM has to be connected to L.

Yeah I understand that at the thermostat end, I mentioned the boiler end. If you look at the photos, there’s a link in the room stat terminal, which on some models of boiler will call for heat all the time.

 

[EFLImpudence]

Yeah I understand that at the thermostat end, I mentioned the boiler end. If you look at the photos, there’s a link in the room stat terminal, which on some models of boiler will call for heat all the time.

That's not the room stat terminals; it is the hot water ones.

 

[Harry Bloomfield]

I wonder if the neutral, is not connected to anything at the other end of that cable? The original stat, appears to be a mechanical stat, so would appear to work without the neutral but the fancier, newer unit, being electronic, will need the neutral.

Another possibility, is that the OP has damaged the new stat., randomly connecting the wiring to it..

 

[EFLImpudence]

I wonder if the neutral, is not connected to anything at the other end of that cable?

D'oh that's it.

They grey is connected to 19.

 

[CountryFan]

That's not the room stat terminals; it is the hot water ones.

Looks like it says room stat to me, my bad

 

[EFLImpudence]

Looks like it says room stat to me, my bad

Oh. I was looking at the red link in 17 & 18. I think I had better give up.

 

[ericmark]

White, Brown, and black wires into a connector block so can safely test them, and use tester to see which are line, two likely faults, either White is not connected to neutral, or Black not Brown is feed.

 

[Willr2]

Hi not sure if anyone can help I’m also trying to connect a Meross MTS200 - I’ve connected the black wire to the Neautral, brown to the live and I have a grey wire that I’ve put in the NO - can get the display to work however I can’t get the boiler to lock in to heat up - any ideas what I’m doing wrong??
I cant find any diagrams for this type / colour of wiring

 

[flameport]

black wire to the Neautral, brown to the live and I have a grey wire that I’ve put in the NO

How were those wires connected to the previous thermostat?

 

[Willr2]

There was only 2 wires connected- black and brown
When I connect just the wires it does connect the display but doesn’t boost the boiler

I have got dual thermostats - does that make a difference? They were wired both the same

The grey wire was loose in the cavity with the earth wire

 

[CountryFan]

There was only 2 wires connected- black and brown
When I connect just the wires it does connect the display but doesn’t boost the boiler

I have got dual thermostats - does that make a difference? They were wired both the same

The grey wire was loose in the cavity with the earth wire

Completely wrong.

Black is switched live, the brown will be permanent live. That thermostat needs a permanent live and permanent neutral to work. You need to ascertain if the grey is connected the other end, ime they’re not.

 

[ericmark]

One, it is bad practice to ask question on someone else thread, as the answers to one may not be the same as the answer to other person asking, so I am replying to @Willr2 with this.

Brown and Black goes to 3 NO and 5 COM, as to which way around, does not really matter.

We have no idea if the boiler is controlled with low voltage (230 volt AC) or extra low voltage (around 24 volt), however since it has powered the display, it seems likely low voltage. Personally, I would measure with a meter of some sort. The grey wire may well be neutral, but we don't know that.

The same with the bare wire, seems likely it is earth, but we don't know that.

To measure one need a reference point, seems likely my body is earth so holding a meter with a non-contact voltage option, one should be able to work out which one (black or brown) is permeant line. But a NCV tester can give false results, here my tested is being held to my laptop, which is powered from a SELV supply, but it is showing 3 out of 4 bars, the red LED is flashing and the beeper going as if my laptop is live. So care is needed, with one to 4 bars one should be able to show which wire brown or black, is showing the highest reading, so likely the line feed.

But I tend to look for a known good earth, as a reference point, and use plug in leads and measure the voltage. The neutral must come from the same circuit as the line, so the hope is the grey is neutral, but need to test.

There is no real reason why the thermostat should not be supplied from a different circuit to the boiler, however this is frowned on, even if a Nest Gen 3 with the thermostat being powered from a USB transformer is doing just that.

 

[CountryFan]

One, it is bad practice to ask question on someone else thread, as the answers to one may not be the same as the answer to other person asking, so I am replying to @Willr2 with this.

Brown and Black goes to 3 NO and 5 COM, as to which way around, does not really matter.

We have no idea if the boiler is controlled with low voltage (230 volt AC) or extra low voltage (around 24 volt), however since it has powered the display, it seems likely low voltage. Personally, I would measure with a meter of some sort. The grey wire may well be neutral, but we don't know that.

The same with the bare wire, seems likely it is earth, but we don't know that.

To measure one need a reference point, seems likely my body is earth so holding a meter with a non-contact voltage option, one should be able to work out which one (black or brown) is permeant line. But a NCV tester can give false results, View attachment 389557 here my tested is being held to my laptop, which is powered from a SELV supply, but it is showing 3 out of 4 bars, the red LED is flashing and the beeper going as if my laptop is live. So care is needed, with one to 4 bars one should be able to show which wire brown or black, is showing the highest reading, so likely the line feed.

But I tend to look for a known good earth, as a reference point, and use plug in leads and measure the voltage. The neutral must come from the same circuit as the line, so the hope is the grey is neutral, but need to test.

There is no real reason why the thermostat should not be supplied from a different circuit to the boiler, however this is frowned on, even if a Nest Gen 3 with the thermostat being powered from a USB transformer is doing just that.

Existing setup appears to be zonal heating and existing thermostats are stating 230vac