Smart thermostat mts200

[jayknucklez]

I have a refoss mts200 smart thermostat, ive wired it in and now the voltage keeps dropping every three seconds or so, therfore the thermostat keep coming on and off, ive put my multimeter on the terminals and the voltage is up and down but its steady with the old thermostat connected.

 

[CBW]

Sounds like it’s faulty. Any photos of previous wiring, or are you happy it’s the same?

 

[jayknucklez]

It was a old honeywell thermostat with a dial with just a live and neutral

 

[CBW]

It was a old honeywell thermostat with a dial with just a live and neutral

If it had just a live and neutral, then where has the extra wire come from in your photo? If it was a 2 wire installation on the Honeywell, you would have a live and switched and could have used the wrong wire.

 

[jayknucklez]

This is the original thermostat wiring, the yellow wire isn't used but is still there

 

[RandomGrinch]

This is the original thermostat wiring, the yellow wire isn't used but is still there

As @CBW says above, you have wired the stat incorrectly; the blue is not a Neutral.
With your old stat connected, the red wire was the Live, and the Blue was a switched Live.
You need to find how the other end of the cable is connected to the boiler/wiring centre.
Then, you can reconnect the wiring accordingly - changing the blue to a Neutral and the yellow can become the switched Live.

 

[jayknucklez]

Thanks, just one more question, where would the switched live go on the new thermostat?

 

[CBW]

Thanks, just one more question, where would the switched live go on the new thermostat?

To the NO.

 

[RandomGrinch]

Thanks, just one more question, where would the switched live go on the new thermostat?

The way you had the wires connected in your first image, was how it should be - if only the wires on the other end of the cable were correct!

Find the other end of the cable.
Where the blue wire is connected to the switched Live, swap that for the yellow wire.
Then find a neutral terminal, to put the blue wire into.
Leave the red wire where it is, connected to Live.