Retrofitting smart controller to combi boiler (Sabre HE 29)

[Aussie_Peter]

I have a Sabre 29HE gas combi boiler with a mechanical timer. The system has no external thermostat controlling the boiler and I was considering adding a Smart thermostat/controller (ie Hive or similar) to it to allow it to be controlled remotely (ie using a phone app).

Can anyone advise if this is a straight forward install that a competent DIY'er could do or if this is a job for a spark?

 

[RandomGrinch]

I believe from the manual, that the external case does not form part of the room sealing of the appliance - if it were, you would have needed an RGI to assist with installing an external thermostat.

To wire up a new thermostat, you are looking for a terminal block to connect the external controls to...

An important note, it states that the controller should be 'volt free switching' - the control circuits may be using something like 24V; a mains switching 'stat could damage the boiler.
For example a Nest, or a single channel Hive would be ok, a dual channel Hive would not be!

 

[Aussie_Peter]

I believe from the manual, that the external case does not form part of the room sealing of the appliance - if it were, you would have needed an RGI to assist with installing an external thermostat.

From the manual, you are looking for a terminal block to connect the external controls to...

View attachment 321172

An important note, it states that the controller should be 'volt free switching' - the control circuits may be using something like 24V; a mains switching 'stat could damage the boiler.
For example a Nest, or a single channel Hive would be ok, a dual channel Hive would not be!

Thanks for the knowledgeable update

The "volt free switching" is not something I'm familiar with. I was considering using this but can't see anything about "volt free" - do you think it would be suitable?

https://www.amazon.co.uk/Thermostat-Underfloor-Multi-room-Compatible-Assistant/dp/B0B96YGWTZ/

 

[RandomGrinch]

The "volt free switching" is not something I'm familiar with. I was considering using this but can't see anything about "volt free" - do you think it would be suitable?

Yes it does have 'volt free switching'...

You would connect the two black wires in the boilers terminal blocks, to NO (terminal 3) and COM (terminal 5) on the Meross (manual attached).

Ideally, you should use a 4 core and earth flex, to make the connections between boiler and stat.

 

[ericmark]

First thing I looked for, is does the boiler modulate and the manual shows

so output between 14.28 and 28.30 kW, and it refers to a latent heat collector, so it does seem to be a condensating boiler. So the main control is the thermostatic radiator valve, (TRV) basic idea is, hot water is pumped to radiators, these warm the room, and cause a air flow within the room, when the return air heats the TRV it closes, not simply open/closed but gradually regulates the flow, as the pressure raises the by pass valve opens, allow hot water directly back to boiler, so the return water gets hotter, and the boiler senses this and reduces output, once the output can't be reduced any more, then the boiler starts to cycle off/on, so we fit a wall thermostat to switch off the boiler when the cycling gets too much, but room temperature is controlled by the TRV not the wall thermostat.

The problem is the TRV takes time to open and close, so the flow needs restricting with a lock shield valve to give the TRV the time it needs to adjust. So the user is left with two adjustments and nothing to tell them which to adjust, and a TRV with *123456 does not really help, one wants some thing like 20ºC, so by moving from mechanical to electronic you get the temperture displayed as 20ºC. So direct or with an app you can see what is going on, and with the app you can see target and current, and in cold weather current should never exceed target, if it does the lock shield needs closing a little, so it also helps set the lock shield valve.

Fitting is by one screw ring, no wiring up, cost does vary £15 to £80 depending on what features, so can link to a hub/wall thermostat to tell the boiler when to switch off/on, and I moved one electronic radiator to radiator to set lock shield valves, once set the old mechanical worked A1 if you always want room at same temperature. But you can also set time and some do connect to internet so can be remotely controlled or use geofencing. And no wiring required, and they help the boiler extract the latent heat.

I fitted in mothers house with idea of fitting a wall thermostat latter, but once set worked that well never bothered with new wall thermostat.

 

[Aussie_Peter]

First thing I looked for, is does the boiler modulate and the manual shows View attachment 321181
so output between 14.28 and 28.30 kW, and it refers to a latent heat collector, so it does seem to be a condensating boiler. So the main control is the thermostatic radiator valve, (TRV) basic idea is, hot water is pumped to radiators, these warm the room, and cause a air flow within the room, when the return air heats the TRV it closes, not simply open/closed but gradually regulates the flow, as the pressure raises the by pass valve opens, allow hot water directly back to boiler, so the return water gets hotter, and the boiler senses this and reduces output, once the output can't be reduced any more, then the boiler starts to cycle off/on, so we fit a wall thermostat to switch off the boiler when the cycling gets too much, but room temperature is controlled by the TRV not the wall thermostat.

The problem is the TRV takes time to open and close, so the flow needs restricting with a lock shield valve to give the TRV the time it needs to adjust. So the user is left with two adjustments and nothing to tell them which to adjust, and a TRV with *123456 does not really help, one wants some thing like 20ºC, so by moving from mechanical to electronic you get the temperture displayed as 20ºC. So direct View attachment 321184or with an app View attachment 321185 you can see what is going on, and with the app you can see target and current, and in cold weather current should never exceed target, if it does the lock shield needs closing a little, so it also helps set the lock shield valve.

Fitting is by one screw ring, no wiring up, cost does vary £15 to £80 depending on what features, so can link to a hub/wall thermostat to tell the boiler when to switch off/on, and I moved one electronic radiator to radiator to set lock shield valves, once set the old mechanical worked A1 if you always want room at same temperature. But you can also set time and some do connect to internet so can be remotely controlled or use geofencing. And no wiring required, and they help the boiler extract the latent heat.

I fitted in mothers house with idea of fitting a wall thermostat latter, but once set worked that well never bothered with new wall thermostat.

Are you suggesting programmable TRV's instead of smart switch on the boiler? I had thought of doing doing that and just turning them all off at certain times, but that would require boiler to in effect be "always on" and that might increase gas consumption. It would also be more costly that the smart switch

 

[RandomGrinch]

Are you suggesting programmable TRV's instead of smart switch on the boiler? I had thought of doing doing that and just turning them all off at certain times, but that would require boiler to in effect be "always on" and that might increase gas consumption. It would also be more costly that the smart switch

No, you would still need a smart thermostat, in addition to the TRVs.
The smart TRV will send a message to the thermostat and this in turn, will call for heat from the boiler.
If you are interested in smart TRVs, you could look at a single channel Hive, or a single channel Drayton Wiser. Both of these are compatible with smart TRVs, that you could purchase at a later date.

...and don't mention a Nest to @ericmark !

 

[ericmark]

Yes I hate my Nest, but it is because it did not do what it should that I have learnt as a result.

 

[Harry Bloomfield]

The "volt free switching" is not something I'm familiar with.

The 'volt(age) free', simply means it needs to have a pair of contacts, free of any voltages, which simply make and break. They should have no voltage on them, until connected to another circuit. One wire with voltage on to the switch, one wire coming back, which is switched.

 

[Aussie_Peter]

So my last question - any recommendations for a smart controller to do the job?

 

[RandomGrinch]

So my last question - any recommendations for a smart controller to do the job?

If you are interested in smart TRVs, you could look at a ..... single channel Drayton Wiser. Both of these are compatible with smart TRVs, that you could purchase at a later date.

 

[ericmark]

You will need to do some reading, I thought I could set the thermostat to switch on when either my wife's or my phone is within 20 miles, but Google Nest does not have this feature. I am told some do.

The Honeywell Evohome was one of the first, and seems better than others at local control, Drayton Wiser is claimed to have algarithums to work out time to heat room built into the TRV, Tado seem not to say what there system will do, and some bits not available in UK, Hive unlike the rest does not have option of OpenTherm, and wall thermostat needs to be in a room kept below 22 degs.

There is no best, they are all diffrent. EPH can combine OpenTherm and on/off switching so boiler OpenTherm and motorised valves on/off but does not connect to TRV heads.

Moes is very cheap. And I use eQ-3, energenie, and Kasa TRV heads. And this is the problem, plumbers/electricians may fit systems, but we still only use what we have in our own homes, and if it works, we take no notice, only when it goes wrong do we look at it. So my old open plan house worked A1 so did not look at heating, mothers house however did have control problems, as does this house so looked into why.

In both cases wall thermostat in the hall. I intend to fit a second in parrellel, but since not done yet, can't say if it will work.