Remote control of heating without Nest/Hive or similar

Sorry this is so long!

Situation: I'm often away from home for a week or more, and want to be able to switch the heating on before I return - but I don't want to go the full Nest/Hive etc or rely on a third-party service.

My last place had a combi gas boiler which fired on demand, if either hot water was requested, or if the central heating came on. No hot water tank. It had a built-in clock/programmer. I found a simple little device [1] that was an SMS-controlled switch, with temperature sensor: I wired it in parallel with the thermostat. So I would leave it with the central heating on permanently, the thermostat turned down to 11 or so - which was reassuring about not letting the pipes freeze. When I was coming home I could send it a text, and it would pretend to be the thermostat feeling chilly, heating came on, everything was great.

Now I've moved. This place also has a combi boiler [2] downstairs, but it also has a hot water tank upstairs; and the system is wired differently. There's a separate programmer [3], the kind that clips onto a back plate, which allows you to set times independently for when the hot water and the central heating come on. This means that you can set the central heating to come on, with the hot water off - but I think this is a mistake, i.e. I'm reasonably sure that in that case it would just pump water round the system without firing the boiler to ensure that water is hot. (And there's also a thermostat for the central heating.)

The previous set up was ideal: when I was away, nothing was active unless I sent it a message (or unless it got very cold indeed). But I can't use that here because - unless I've misunderstood - just overriding the thermostat to activate the central heating wouldn't work unless I also have the hot water coming on regularly.

There seem to be a lot of wifi-connected thermostat things - like Nest - but AFAICT these would have the same problem - and in any case I don't want anything that relies on a remote service (or ties me into Google/Amazon/etc).

The options I can see are:

- find a "local" WiFi programmer (not thermostat), designed to let you use a smartphone to control it in the house - and then figure out remote access into my home network. So far I've only found a "programmable thermostat" with this option[4], but not a two-channel programmer.

- use the same approach as I had before, so that I can effectively turn up the thermostat remotely by SMS. This would I think require to have the hot water switched on by the programmer at least some time every day while I'm away, so not a very efficient solution.

- use the same approach as I had before, but with two channels, so that I can control both the hot water and central heating by SMS. Ideally separate control of them; but failing that if I can switch both on at once remotely, that would work for me.

- find a miracle product that does most of what I want. E.g. I briefly thought the heatmiser range might be suitable, but they rely on a central cloud service. At work the office has a remote (RF) programmer - if one of these had an open protocol so that I could set up another controller that would work. Or using OpenTherm???


My questions:

1) Have I correctly understood that the system in this new (to me) house requires separate control of hot water and central heating - whereas all the new control stuff seems to assume that hot water will operate on demand from heating, and therefore it's only necessary to control the thermostat?

2) ... and is that the difference between a "programmable thermostat" and a "two channel programmer"?

3) Supposing I installed a separate SMS-controlled system. Is there a reason why I couldn't wire it in parallel with the existing programmer, so that it can on demand short out (that is, switch live to) HW and CH as required? Should this bother the programmer that might also do that?

4) ... and if I took that approach, is that 240V or something more like 24V (I need to make sure the relays are appropriate)?

5) On the other hand, has anyone come across a WiFi two-channel programmer (working locally not via a central server)?

Many thanks in advance for any light you can shed.

David


[1] https://store.open-electronics.org/GSM_Remote_Control_Temperature_Control
[2] Vaillant ecoTEC plus VU GB 624/5-5
[3] Horstmann Centaur Plus C21
[4] - e.g. http://www.esicontrols.co.uk/esrtp5wifi.html - also I think Heatmiser used to do a "PRT-TS WiFi" but it looks like this is discontinued

If you have a Vaillant 624, it's not a combi boiler, it's a system boiler. You should have completely independent control of heating and hot water, so if you turn just the heating on, just the radiators will warm up, and if you turn just the hot water on, just the cylinder will warm up. Turn both on and both will warm up. You won't have a situation where you can circulate the system without the boiler firing. All of the current crop of WiFi based programmers are variable of maintaining this level of control.

A programmable thermostat allows you to program times & temperatures. A 2 channel programmer allows control of times only and must have a separate thermostat connected to complete the system. Things like Nest & Hive combine both functions - they are a programmable thermostat for the heating, and have a second channel for programming hot water.

I'm not aware of any SMS based systems still in production. It's a very old hat way of doing things. Times have moved on, we have the Internet now.

You'll need 230v controls

What's your aversion to cloud-based products? They just rely on the cloud for remote access. If you're in your home, you'll still have control even if the cloud stops working.

Hi Andrew, thanks for replying.

So to be clear, if the 2 channel programmer is set to have hot water switched off, and central heating on - with the thermostat turned down; and it is left like this for a long time so that the any stored water will have cooled down; and then the thermostat is turned up; you would expect that the boiler will fire to heat water to be pumped around the central heating?

A programmer is basic a time switch, I suspect some thing like Sonoff can be used to turn on/off DHW or CH, but the question is if enough is saved to be worth it, Moes does a wifi thermostat and I have found them at £25 or less, so seems rather pointless to reinvent the wheel.

The problem I have found through my life, is if you assemble some thing which is not standard, then others have problems repairing it, this caused my wife the problem when I went to the Falklands for 6 months, if some thing I assembled when wrong she had to wait for my return.

I have a PLC sitting in a box, which I had kept with the idea of automating the home, but it has stayed in the box, as should I die, and I am nearly 70, who will repair it?

Deeteebee said:

Hi Andrew, thanks for replying.

So to be clear, if the 2 channel programmer is set to have hot water switched off, and central heating on - with the thermostat turned down; and it is left like this for a long time so that the any stored water will have cooled down; and then the thermostat is turned up; you would expect that the boiler will fire to heat water to be pumped around the central heating?

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Yes, correct

Hmmm. I tested with both Hot Water and Central Heating switched off at the two-channel programmer. When the house was cold, switched on Central Heating (and cranked up the thermostat to be sure). Boiler didn't react. I gave it half an hour before switching on Hot Water as well; then the boiler fired.

Does this mean my system works differently? Or that the programmer has been wired incorrectly?

Thanks again for any info.

We have plans, S Plan, Y Plan, W Plan and C plan for example, the C Plan has been upgraded over the years, so now three versions.

The programmers of yesteryear could be set to 10 or 16 programs, to be frank they counted off so not really that many options, often both a mechanical and electrical switch to swap between the two. The reason was some boilers had no cool down, and you could not turn off DHW when using CH, the DHW was thermo syphon some times called gravity, so if boiler runs DHW heats up, but the CH used a pump, so in theory if pump not turned on no CH, however in practice upper floors would still thermo syphon specially if they had been on.

The latter versions allowed summer use of a tank thermostat, and in some cases a motorised valve for DHW so the temperature of the DHW could be controlled. But the old C Plan often only way the boiler could cool down was thermo syphon so often no motorised valve.

The Y and W Plan also default DHW but use a three port valve, the W Plan is used when the DHW tank is very small, i.e. built into boiler, in the main we see the Y Plan with three port valves and it has three positions, default DHW, then half way both and all way CH, the advantage is water can pass through the pump even when off, and allow boiler to cool without any run on.

Then there is the S Plan, this uses two port valves, and the system if the thermostats control the valves, then the valves control the boiler.

Today we have also some hybrid systems, EPH for example do thermostats that work in master slave configuration and the motorised valve is either open or closed, but the boiler is controlled by the ebus with a variable output.

Before you can design an electrical control, you need to know how plumbed and how the boiler is controlled, some boilers can use 230 volt (low voltage) or 24 volt (extra low voltage) or ebus control, so simply saying I have a xyz boiler is not enough, and I got caught out with Worcester Bosch as the latter versions of my mothers boiler had the option for ebus control, but hers did not. As an electrician I can't say what boilers do what without reading the manual, and you can read that your self.

The problem is there does not seem to be any one system fits all, if the house is spit into zones with motorised valves then you do not in theory need to control individual rooms using TRV heads, so EPH thermostats don't seem to work with TRV heads, and of course the same in reverse, a system designed to work with TRV heads like for example Hive, is not designed to work with zone valves, there may be a work around, but some systems like Nest don't work with either zone valves or TRV heads other than for CH and DHW.

If the boiler is designed to gain the latent heat, then turning the boiler off/on can be counter productive, it may give very good control using mark/space ratio to avoid over shooting, but it can also cause the boiler to run inefficiently. So working well, and working efficiently are not the same thing.

In my old house the central heating worked, so never really thought about it, mothers house didn't so when my dad died it was down to me to sort, and I made mistakes, one how much heat is gained by bay windows, two how fast the house cools, three how fast a radiator cools, I had all big ideas about geofencing, which I realised would never work as the controls are too slow to act.

The Energenie MiHome TRV head I selected was OTT with anti-hysteresis software so on selecting 20°C it could take 3 hours or more before the room hit 20°C so I would cheat and set to 22°C for an hour, then 20°C, but this will not work with geofencing direct to the TRV.

However same TRV heads in this house, with oil instead of gas boiler, so boiler does not modulate, and I use Nest Gen 3 to geofence, and the anti-hysteresis is not good enough, as radiators are hotter and so store more heat, and my hall over shoots unless I set temperature at 0.5°C increase per hour.

Every house is different, what works with one house may not work with another, we call the guys who do this heating and ventilating engineers, and to me engineer means trained to level 5 or above, i.e. a degree. Yes I have a degree, but not in heating and ventilating, and the more I learn the more I realise I don't know.

But the big question to ask yourself, is if you are ill, who will fix it?

ericmark said:

and the more I learn the more I realise I don't know.

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This goes the same about women!

Andy

HERTS P&D said:

This goes the same about women!

Andy

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And always will

If it is a 2 channel programmer you have then you can just control the heating via SMS and leave the DHW to come on as you wish via the programmer. My set-up was wired from an alarm output to the programmer many moons ago allowing me to just turn the heating on and off via text. However, 12 months ago I moved the heating to Nest due to a new boiler and cylinder being fitted.

During the summer my DHW is simple timed, 5 times a week at ½ hour each time, not really ½ hour as after 20 minutes the boiler switches off and starts to cycle, and if it switched on again only for a few minutes before ½ hour time is over. And my tank is not very well lagged. With such little time required to maintain water to temperature if I had a tank thermostat I would not bother with any timed switch on.

I also used Nest Gen 3, which has minimum time slot of ½ hour, which is better than what was there, with minimum of one hour a day.

Central heating wise, the geofencing has not been that successful. The problem is temperature control. Turn on heating and it over shoots, and the cooling time of the hall where the wall thermostat is mounted, is too slow. And all other rooms have alternative heating, or outside doors which are used. In my house the official front door into hall is never used. And hall is the most central point of house, and is the best average temperature from all rooms, but cools slowly.

My mothers house also the hall seemed not the best location in some ways, wind direction and sun could result in kitchen getting cold, so that one fitted second thermostat in kitchen in parallel with hall one.

But geofencing really need one thermostat, did try using the TRV heads which will geofence, but again not much good as on a temperature change they take too long to adjust temperature. Be it over shooting or slow time never got geofencing to work. And heating cost is around £2 per day in winter. At £2 a day that means geofencing likely saves 50p at most per day. This winter we have both left the house for over 3 hours and under that time not worth it turning off, around 5 times, so geofencing has likely saved £2.

If it is a scheduled vacation of the home, i.e. going to work, simple timed control likely works better. If you leave the house at 8 am the heating can go off likely 7:30 am and no latter than 8 am, but geofencing will not turn it off until you have travelled some miles from home, so likely nearly 9 am before it switches off. So even with a varied return from work, the hour or so saved, is really nothing.

And all this auto technology does not work when my wife says, darn it, left my phone at home.

As to actually getting the phone out to control house temperature, yes in the summer I would look on phone and if the TRV showed over 26°C current, I would energise the plug in wifi switch/monitor to start the AC unit, because I can monitor use I know if actually energised, so know the command has worked. And returned home to a cooler room than it would have been had I not switched it on, only reason not left switched on, is the bottle for condensate is 2 litre and it would over flow if left on. The exhaust for AC goes up the flue. I have never got my phone out on a cold day to turn on central heating before I get home. In the main I have not switched it off, gone out in a hurry, and so unless geofencing does it not turned off.

Is it worth spending even £50 on remote controls to save £10 a year? Over night when heating turned off, in the morning rarely cooler than 17°C so room on average just 1.5°C cooler when heating turned off, so energy saved is so small is it really worth worrying about?

Its vaillant then look at their Vaillant controls as it will also allow the boiler to do full modulation with weather compensation, the VR920 module will add internet connectivity to the existing system. Its not a smart setup, just has remote access, if internet goes down it will continue doing what it was last setup to do.
Vaillant does not officially support Opentherm so their modules are the best you can get.

If you do not need internet connectivity the VR720F has ability to set holidays/away days etc, so if you know you will be away for 7 days you set start/end dates and it will stay in setback until then etc but add the VR920 you can control it all though phone app but does not rely on it.

VR720F SensoCOMFORT WC + VR920 internet module etc.

rbranco said:

Its vaillant then look at their Vaillant controls as it will also allow the boiler to do full modulation with weather compensation, the VR920 module will add internet connectivity to the existing system. Its not a smart setup, just has remote access, if internet goes down it will continue doing what it was last setup to do

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@rbranco thank you I'll look into this.

Twenty Four said:

If it is a 2 channel programmer you have then you can just control the heating via SMS and leave the DHW to come on as you wish via the programmer. My set-up was wired from an alarm output to the programmer many moons ago allowing me to just turn the heating on and off via text. However, 12 months ago I moved the heating to Nest due to a new boiler and cylinder being fitted.

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Yes, that's just what I want.

My problem is that AFAICT when I ask for CH (on the 2 channel programmer) the boiler doesn't respond - so it seems we can only get heating if we're also explicitly asking for HW. I'm not sure if that means the programmer (or boiler) has been configured incorrectly, since both what you and @muggles have said suggests that this shouldn't be the case?

Deeteebee said:

Yes, that's just what I want.

My problem is that AFAICT when I ask for CH (on the 2 channel programmer) the boiler doesn't respond - so it seems we can only get heating if we're also explicitly asking for HW. I'm not sure if that means the programmer (or boiler) has been configured incorrectly, since both what you and @muggles have said suggests that this shouldn't be the case?

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It means that the wiring of the zone valves is probably incorrect or the microswitch in the CH zonevalve is broken.