Replace TLX 2259 thermostat with BHT-3000 wiring advice pls

Joined
12 Aug 2020
Messages
2
Reaction score
0
Country
United Kingdom
Hi I want to replace an old Sunvic TLX 2259 with a MoesGo BHT-3000.

I found similar threads for other models but responses seemed to suggest starting a new thread is the way to go.

The Sunvic was wired like this (3 wires plus earth) :



And here are the terminals for the new thermostat:


Any advice gratefully received, thanks.
 
Sponsored Links
Red - L
Blue - N
Yellow - 2
Fit a jumper wire from L to 1
Park earth in a terminal block
 
Sponsored Links
There should be a sensor under the floor to stop floor over heating, they seem to work without the sensor connected in the main, however the difference between on and off may be unsuitable. Depends on set up, the idea with on/off thermostats with an oil boiler or old gas boiler was often to control room temperature, but with new gas boilers, the TRV should be controlling room temperature and the wall thermostat is only there to switch off heating on warm days, not to control room temperature, if it is used to control room temperature it can end up switching off/on too often and each time it switches off any heat in the boiler goes out of the flue.
 
Thanks guys for the info. There are 3 versions of this stat, this one is for gas boiler/heating systems which is what I'll be using it for; another is for electric heating, and the third for under floor heating.

Hopefully this is the right one, I'll wire it up and report back.
 
Electric heating version often carry more current, but would still work. Under floor heating version will likely work, but now looking at the hysteresis, with an on/off boiler control, now rare with gas, each time the boiler turns off, any heat in the boiler is lost out of the flue, and each time it turns on it runs flat out until the return water gets warm, so turning off/on wastes energy, but to stop the room temperature over shooting some thermostats use a mark/space ratio as they approach the set temperature so the temperature does not over shoot, although it does stop the over shoot, it also wastes energy due to method used.

So in the main we control room temperature with thermostatic radiator valves (TRV) however unless linked to the boiler electrically as summer arrives the boiler will start cycling on/off as it has no way to know when no longer required, it is controlled by return water temperature so no circulation means no control.

So we fit a wall thermostat, and we fit it in a room kept cool, so it can be set low enough to switch off boiler in the summer, and also it needs to be on a lower floor, with no outside doors, this is often not possible so we use a compromise and fit in the hall, and also use a TRV in the hall, but of course need setting to same schedule.

So all the wall thermostat does is turn off boiler when not required, it does not control room temperature, that is what the TRV is for, so in real terms having a large difference between on temperature and off temperature works well, with the old mechanical thermostat not connecting the neutral resulted in it working very well.

But with oil boilers or under floor heating and open plan houses we want that difference to be as little as possible.

There are some clever thermostats which record how long it takes to heat the room, and switch off allowing for the heat left in the radiator, drayton TRV electronic heads do this, as does the Nest thermostat, there are also thermostats which don't simply turn boiler off/on but up/down often using opentherm protocol again Nest is one example. And there are wall thermostats which connect to the TRV heads so know when not required Hive is an example of this.

But people go to university and train as heating engineers so they can select the best options, they need over level 3 to be considered an engineer, although I have trained over level 3 it is not in heating, I am more into near enough engineering.
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Back
Top