Smart thermostat help

[Nwr161282]

I am looking to get a smart thermostat system fitted either hive or nest. I would like to make sure I purchase the right thing. I currently have an oil boiler controlled by a 7 day digital programmer. I have 2 water tanks and a hot water cylinder in my loft. I can heat my hot water on its own but when I turn my heating on the hot water comes on automatically with it. There is a pump mounted next to my boiler but I believe that is uses for the central heating system.

What type of system do i have? And will the smart thermostat work for my system.

 

[muggles]

Sounds like you might have a gravity hot water and pumped central heating system. Does your cylinder have a thermostat strapped to the side of it? A few photos of boiler/valves etc would help

 

[ericmark]

Your description matches my system and I have Nest Gen 3 fitted. So do you have a thermostat on your domestic hot water, or is it simply timed in summer? It would seem likely you have a C-Plan.

This is a plan for when there is no thermostat on the hot water tank, i.e. the most basic system. The main point is the Boiler is feed from the Com terminal on the Nest heat link, with most other systems the Com is internally connected to line in, or to other com so the Nest is unusual in that it allows one to connect it up this way.

To be frank the Hive system of connecting to the TRV heads is far better than Nest, with Nest it is claimed to work with Energenie MiHome TRV's but it has had the support withdrawn, so cheap eQ-3 works just as well not connected to Nest as the MiHome but a lot cheaper, so if you want each room independent Hive may be better, however Hive can't be wired as shown with Nest, it needs a tank thermostat to work, OK Nest would also be better with tank thermostat but it does not NEED it.

 

[ericmark]

There are other "Smart" systems, depends what you want to do, EvoHome is considered as one of the best, but much depends if you want to control each room independent or just system as a whole. Do you want the domestic hot water controlled by the "Smart" system?

I am an electrician not a heating engineer, I was told when I came to do mine that there was no boiler run on to allow it to cool, so it needed the unrestricted connection to cistern to allow boiler to cool, and adding a motorised valve to DHW output was not a good idea. In winter the DHW is switched off, in summer ½ hour Tuesday, Thursday, and Saturday then Sunday 1½ hour to ensure water gets hot enough to stop legionnaires. If I could get a three core and earth boiler to cistern it would be a lot better in summer to have a thermostat on the tank.

Mine also heats a flat under the house, so added motorised valves on the two outlets as it was back feeding and we could not run one without the other. I have found in the past switching off the pump is OK if system is cold, but once warm it continues to heat upper floors with thermo syphon.

Main reason for fitting Nest Gen 3 for me was only two wires between where the boiler is, and where I want control, this is now the T1 and T2 wires, it was not fitted because I wanted the "Smart" features. The Energenie MiHome TRV heads came from the last house, I could I am sure set up GeoFencing with both Nest and MiHome so heating only comes on when I get home, but only set up on Nest at this time, and not as good as expected because of where the thermostat is situated. Being in the hall heat from radiator goes upstairs, so slow reaching the thermostat with two doors between thermostat and radiator, morning the temperature is lifted 0.5°C an hour for three hours so over night at 17°C then 18.5°C, 19.0°C, 19.5°C and finally 20°C the TRV heads in other rooms keep them spot on temperature, without the stepped raise it tends to over shoot then boiler turns off for an hour or so in which time other rooms get too cool. This is what happens if I go out, the GeoFencing means heating turns down, then when it returns to comfort setting it over shoots. I know this is due to thermostat location, but it is common to have thermostat in the hall.

With last house with gas modulating boiler the TRV heads did a good job without needing a "Smart" wall thermostat, which is why I ask, what you want it to do? I have just asked what is the temperature in this house, and the Nest mini has called out the temperatures of 4 TRV heads and the wall thermostat, not tried to alter temperature with Nest Mini I am sure I can, the thing it will not do is close internal doors, so how it works varies due to if doors open or closed. It was bought because no radio reception here, not to control heating with, however it raises a good point.

What works with what, I wanted a remote controlled socket to control mothers alarm, and the whole of the central heating has revolved around that, as TRV used the same hub as sockets and so on. So back to what do you want it to do?

 

[Nwr161282]

I am currently away from home so unable to check my system fully. But I do not think there is a thermostat on my hot water cylinder its self. The house used to have a coal fire with back boiler. The pipework from the back boiler has a thermostat just before it T's into the oil boiler feed and return lines that heat the water cylinder.

My reason for wanting the smart feature is that I work away alot and the electrical power in my area during winter is prone to the odd blip which resets my controller settings. So I'd rather control my whole heating and not just individual rooms.

 

[ianmcd]

My reason for wanting the smart feature is that I work away alot and the electrical power in my area during winter is prone to the odd blip which resets my controller settings. So I'd rather control my whole heating and not just individual rooms.

Just buy the Hive dual channel and set it to gravity HW, couldnt be simpler

 

[Nwr161282]

Just buy the Hive dual channel and set it to gravity HW, couldnt be simpler

That's the answer I was looking for.

 

[ericmark]

Just buy the Hive dual channel and set it to gravity HW, couldnt be simpler

How? He will have two items to power, the boiler, and the pump, with central heating both need power, with domestic hot water only the boiler is powered.

You have 4 terminals clearly the DHW NO goes to boiler, but how can you power the pump only when CH is called for? You need access to the com terminal which you have not got. Nest will work as you can connect com to boiler, Hive will not as com internally connected to line. To use Hive you will need to add a relay or tank thermostat.

Maybe I am wrong, look forward to seeing a wiring diagram for Hive like the one I have given for Nest.

 

[ianmcd]

How? He will have two items to power, the boiler, and the pump, with central heating both need power, with domestic hot water only the boiler is powered.

You have 4 terminals clearly the DHW NO goes to boiler, but how can you power the pump only when CH is called for? You need access to the com terminal which you have not got. Nest will work as you can connect com to boiler, Hive will not as com internally connected to line. To use Hive you will need to add a relay or tank thermostat.

Maybe I am wrong, look forward to seeing a wiring diagram for Hive like the one I have given for Nest.

It is exactly the same as any Gravity HW boiler , just because it is oile makes no difference, HW on to fire the boiler and CH on to power the pump, set Hive to Gravity and when the CH is called for the HW will be called for at the same time, you can not get CH without HW on a Gravity HW system, you dont need a COM on the hive dual channel as the links are internal and already made

 

[bernardgreen]

For Eric

 

[Nwr161282]

I've ordered up the Hive Heating and hot water so will let you know how i get on once its fitted

 

[ericmark]

This is the old C-Plan before the tank thermostat was added, it was rather Heath Robinson in those days, the wall thermostat ran the pump and the boiler was kept hot when ever the timer was calling for heat. So the tank thermostat was added.

This was a major step forward, by using both the NC and NO contacts of the tank thermostat the boiler only ran when required and could be used in the summer for DHW only, but both diagrams rely on having separate time controller, room thermostat and tank thermostat. But latter would work with both Hive and Nest.

However because Nest gives access to the com terminal in the same way as the tank thermostat does this means it can be wired this

way, so in summer hot water only is possible on a timed control only and in winter the central heating can run clearly even with DHW switched off it will still heat, but central heating can be turned off in summer.

So with @bernardgreen diagram if CH NO goes to pump, and DW NO goes to central heating boiler then it would rely on Hive always turning on DW NO when central heating is required, some programmers in fact did do that, there were switches and mechanical links that could be set inside which turned it from 16 option timer to 10 option timer, however although common in the 1980's not seen a programmer with that option for years.

So the big question is if you set the Hive duel unit to gravity are you 100% sure the DW NO contacts will close every time the CH NO contacts close as with those very old programmers? If not then Nest is the way to go, as I am 100% sure that diagram works as that is how wired on my own system. OK I have a few extras as house and flat under house are independent, but that is still the basic wiring used, and it works.

@ianmcd seems to say the DW NO contacts will close when ever CH NO closes, and he may very well be right, but I can't find any Hive instructions to confirm this is the case, these instructions for Hive don't give a single wiring diagram, Nest pages 20 to 25 does give wiring diagrams, OK it does not show the one I have posted, but does show some examples.

I personally think Nest has missed the boat by not having linked TRV heads available for its system, so assuming the Hive TRV heads are used with Hive, then Hive will actually work better, however the inability to access the com and select how it is wired, means it needs relays adding which is a silly idea. Nest has got it right with that at least, the installer has far more options as to how wired. Including hard wiring the thermostat to the heat link if you want so no batteries to change.

 

[ianmcd]

seems to say the DW NO contacts will close when ever CH NO closes

WHAT do you think setting the hive to Gravity HW actually means ? what do you think it does, The OP has asked for a solution, I gave him the simple solution

 

[ericmark]

WHAT do you think setting the hive to Gravity HW actually means ? what do you think it does, The OP has asked for a solution, I gave him the simple solution

Gravity or thermo syphon means the water to the storage tanks heat exchanger if fitted is not pumped, it does not even have to have a heat exchanger, the solid fuel cooker in mothers house did not, the water in the tap and water in the boiler were the same, and it would some times actually boil the water.

As time went on they got rid of solid fuel and at that point a hot coil was fitted, this resulted in the central heating water and domestic hot water being kept separate, however still an open header tank in loft, so hot water not potable. There was also no control of the temperature of the domestic hot water independent of the central heating circulation water, at that time central heating was to give a back ground heat only, still had fires in every room, so central heating came on morning and evening timed only, no thermostats fitted.

By fitting a thermostat to the tank during the summer the boiler could be used for domestic hot water and left on, rather than using simple timed burns, so a thermostat was often added to the tank, also people started fitting thermostats in the house, and using central heating all day long, the next major change was to add a motorised valve to the supply to the DHW hot coil.

The motorised valve allowed one to turn off the DHW heating but continue using central heating, and so one could have cooler DHW.

All these systems were classed as gravity or thermo syphon, there is not simply one C plan but 4 or 5 variations on the C plan with tweaks as time went on.

With the old gas boiler it did not seem to mind being switched off without a cool down period, however the oil boiler retained more heat, so fitting a motorised valve to the gravity or thermo syphon supply could damage the boiler, so oil boilers were not upgraded to the same extent as gas, and many oil boilers have not got a thermostat on the hot water tank, or motorised valves.

After your post I again looked on the net for information about Hive, and if there is an internal setting to switch on DHW with CH, however the instructions simple say

Hive works with most oil boilers and, if you have an existing conventional thermostat or programmer, it can replace either. If you have existing intelligent oil boiler heating controls that modulate your heating, Hive will not replace this functionality. As for installation, our engineers don’t install Hive Active Heating on oil boilers, so we recommend contacting an OFTEC-qualified engineer for help.

I have hunted for a Hive C Plan to see if there is a cylinder thermostat or not, I simply can't find one, as I have said it may work, the DHW may be turned on with CH when set correctly, but there is no official document I can find to say it can be set that way, clearly one can add a relay, so can't actually say Hive will not work even if DHW is not turned on with CH, but it would not be as straight forward to wire up.

There is a long list of boilers mainly Bosch which Hive will not work with, OK Bosch seem to want to force users to use only their systems, specially using the ebus, but main point is Hive is linked to British gas, so if some one has a problem with a gas boiler they can get some one out to fix it, but if they have a problem with an oil boiler, they are looking for an OFTEC-qualified engineer who knows Hive, not so easy to find.

So the question is simple are you 100% sure that Hive when set to gravity will turn on DHW when it calls for CH? Nest I am sure does not, as I have Nest installed, but Nest does not need to as you can wire as I have shown, if you are 100% sure I would agree fit Hive, it's cheaper and has TRV heads that works with it, but if not 100% sure, then safe bet is fit Nest which I know will work.

 

[ianmcd]

Eric please give up, I have told the OP what he needs , please stop trying to complicate everything, your quote in your last post is from BG who own the Hive but will not install on oil, because their engineers are not allowed or qualified to work on oil boilers, regardless of what your gran, your uncle , your father in law your cousin thrice removed your dogs best mate have, if the Op does what I advised it will work and give him everything he wants to do, you say it MAY work , it DOES work, I have fitted them many times, if the OP wanted all the other crap you have added he would have asked for that, He asked how to control a GRAVITY Hw and PUMPED CH system nothing more , and the Hive is more than capable to do it and you keep going on about a Cyl stat, you can not have a Cyl stat on Gravity HW the temp is controlled by the Boiler stat