Wire up Wireless thermostat

[Danielw1978]

Hi all, can anybody advise me how to wire the following:
Neomitis wireless thermostat to a Vaillant boiler?
Here is the boiler wiring diagram
And the thermostat wiring diagram
Any help will be greatly appreciated!

Regards

Daniel

 

[AndyPRK]

You have a thermostat at the moment ?

How many wires does it have? have you got a picture of the inside and outside of it ?

 

[ericmark]

Your boiler can use two completely different types of thermostat, there is a problem with modulating boilers autumn and spring where they continue to cycle when weather is warm enough, to stop this one can fit a on/off thermostat in the coldest room, with no outside door, and no alternative form of heating to turn boiler off when all rooms are warm. During the winter this thermostat should never turn off, the TRV's control room temperatures and the return water temperature controls the boiler. The thermostat should NOT have anti hysteresis software built in, but you clearly want it to fail safe, so in the main wireless not suitable for this application.

There is a completely different thermostat for controlling main room temperature, this connects to Bus shown under the on/off thermostat connection and instead of turning boiler on/off it adjusts the flame up and down.

Some thermostats have both connections for example Nest.

It seems your boiler has three options, however there is a star on the 230 volt option and I can't read what it says, but for either of the other options you need 5 core cable. The thermostat you have it seems is very basic, so X1 L, N, Earth connect to thermostat L, N, and earth, then X100 RT 24 you remove link and connect to 3 and 4 of thermostat.

With more expensive thermostats if the batteries go flat the thermostat base if no signal every 1/2 hour will auto turn off, i.e. it fails safe, cheap one will just continue doing what they were doing before the batteries went flat, so I walked into my mothers house and the heat hit me, with room at 27°C. However the more expensive types also seem to have anti hysteresis software, what this does is start turning off/on before the heat selected so it does not over shoot, this you don't want, whole idea of on/off thermostat is to reduce cycling of the boiler not to increase it.

Having said this I know I have wrong thermostat, it may not be good for the boiler, but it works, to an extent at least, and I intend to move, so not either hard wiring or fitting Nest, in my case should fit Nest, as it can talk to my eTRV heads, but I am too lazy to fit one.

 

[Danielw1978]

You have a thermostat at the moment ?

How many wires does it have? have you got a picture of the inside and outside of it ?

No I don’t have one fitted at the moment.
Daniel

 

[ban-all-sheds]

You have a CH system with no controls?

Why doesn't it run 24x365?

 

[ericmark]

The theory was with a modulating boiler the temperature is controlled by the thermostatic radiator valve (TRV) so there is no need for a room thermostat.

However there is a flaw, once the boiler has throttled back to minimum to reduce the output further it starts to switch off/on, and if after a set time from switching on (time for water to heat up and lift the by-pass valve and return to boiler) the water is still hot the off time is increased, other wise it is decreased, this is anti cycle software. So far so good.

However as the year gets warmer and summer approaches it reaches a stage when heating is no longer required, although it could be made so when the off time reaches a set time it switches completely off, what it could not then do is switch it back on again.

So there are two options.
1) Manually switch it off.
2) Fit a thermostat to automatic turn it off.

So where the latter is used it should be mounted in a room with no outside door, and no alternative form of heating, and in a room normally kept cold enough so thermostat can be set reasonably low say 18°C so on a prospective hot day the central heating will not turn on.

Instead of the TRV where you have an open plan house, you can fit a modulating thermostat, unlike the TRV this can switch on again after it has gone dormant, and like the TRV it will turn boiler up and down, however not suitable where we have rooms with doors.

So next option is eTRV heads which talk to a central controller which in turn tells the boiler what to do, this is what EvoHome does.

There are also systems that use geofencing and other remote controls, be it a simple relay, or eTRV heads, or the hub, but these still have to use the same basic method of control.

So with TRV's you could simply switch on/off manually and let the TRV control temperature, you can swap the TRV head for an electronic one which will control temperature more accurately and allow use of timers for each one, so bedrooms not heated as hot in the day as at night, and reverse for living rooms. Next stage is the wifi TRV head so you can program from PC or phone and also use geofencing. Next stage is TRV heads which connect to a hub, which in turn controls boiler, either simply if any TRV needs heat boiler turns on, or by using follow commands to TRV head and wall thermostat/hub are both singing from same song sheet.

However in real terms this means wall thermostats fall into two groups.
1) Simple wired maybe programmable but job is to turn off heating in summer, saves doing it manually.
2) Super complex with connections to boiler bus and to all eTRV heads.
There are very few places where one would want to use a mid range device, it's all or nothing. With maybe the exceptions being old boilers that don't modulate and open plan houses.

 

[SimonH2]

There are (probably) two ways of connecting your stat.

1) Using the 230V stat connection - but note the "*" which seems to say "variant dependent"
You need 3 cores (plus earth). Link L&N in the stat to L&N at the boiler, link L at the stat to 3, and link 4 at the stat to the RT input on the boiler - "230V AC room thermostat".

2) Using the 24V stat connection
You need 4 cores (plus earth). Link L&N at the boiler to L&N at the stat. Link the "24V DC room thermostat" connections to 3&4 on the thermostat - and remove the link that will be fitted in the boiler.
IMPORTANT - you must not under any circumstances allow mains to get onto the 24V DC stat connections, it will almost certainly blow the circuit board.

In both cases, it's a pity that boiler manufacturers don't provide terminals to provide the power to the stat - so you need to double up in the mains in terminals which can be "fiddly" in some of the cramped spaces they seem to like putting them.

Your local plumbing/heating wholesaler is likely to have the cable in stock.