Thermostat wiring

[Karlosfandango1]

Hello
Can anyone help me understand how to change my RMT230 thermostat to a digital one I have bought? (Moes 009 series Gov thermostat)
It’s for my combi boiler
3 wires at in my RMT one (240v)
White=4
Brown =1
Black =3
Just not sure where they going the new thermostat
Picks below
Old thermostat and new one
Thanks so much in advance

 

[ericmark]

This shows 4 is neutral 1 is line in and 2 is line out to boiler
So wire from 4 goes to 3 on new.
wire from 2 goes to 2 on new.
wire from 1 goes to both 1 and 4 on new, you will need a link wire.

Note old thermostat would work with no neutral, the new one needs a neutral, so I would start with a meter between 4 and 1 and see if you get 230 volt, just in case neutral not connected other end.

 

[Karlosfandango1]

Thank you so much I will give that a try now and let you know

 

[Stuckinarut]

New thermostat requires a permanent live and permanent neutral, so possible to use above, but might also not.

 

[ericmark]

Need thermostat requires a permanent live and permanent neutral, so possible to use above, but might also not.

Agreed, not sure what gain from the change anyway.

The basic idea is the TRV controls water flow to each radiator depending on what the room needs, as the water flow is reduced the by-pass valve opens letting hot water back to the boiler, which in turn reduces output to match the demand.

This has a flaw, there is nothing to turn off the boiler, when all TRV's have closed, so the boiler with cycle on/off all the time, so we need to add something to turn off the boiler when not required. A strategically placed wall thermostat can turn off the boiler when not required, but it can also cause the boiler to fail to gain the latent heat in the flue gases, if switched on/off too often.

So the slewing range, (difference between on and off temperatures) becomes important, too small and the boiler turns on/off too often, and the old thermostats without a neutral have a large slewing range, maybe 2ºC but new ones have a smaller slewing range maybe 0.5ºC, so the old thermostat may be better than the new one.

The system needs balancing, and the wall thermostat set to match the TRV, with a TRV which shows target and current, one can slowly over time get them set spot on, but a TRV which shows *123456 can be used after the lock shield valve is set, but until that has been done, to set two parameters is very hard, as you simply don't know which to alter.

 

[Karlosfandango1]

@ericmark thank you
If I could buy you a beer I would !
Your directions worked - I had already checked and a neutral was in place
You are amazing thanks again

 

[Stuckinarut]

@Stuckinarut thank you
If I could buy you a beer I would !
Your directions worked - I had already checked and a neutral was in place
You are amazing thanks again

TBF it was also @ericmark