Nest learning thermostat

30
Found 13th Feb 2015
Sorry for these silly questions but I don't know too much about central heating systems!

I have a completely gravity based system, tank upstairs, small tank in loft, old thermostat in hallway, boiler downstairs, no diverter valve upstairs (whatever that means)

I have a Programmer that controls hot water and heating

If I turn on just hot water - I get only hot water (rads stay cold)

if I turn on just hot water and heating I get both hot water in taps and heating

if I turn off hot water and turn on heating I get exactly the same as above (Both hot water in taps and heating - is it meant to work like that?!?)

Anyway im interested in having installed and using the nest on the above system if its possible - does anyone know if it would work? And would it mean I would have to have my hot water always on? im abit confused as currently turning central heating on always produces hot water too?

Thanks!
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AskNestThermostat
30 Comments
That's how it should be. Nest is just a fancy thermostat
if you are getting hot water when you have selected heating only then you have a problem...

either incorrect plumbing or a faulty divertor valve...

get that fixed and tell the plumber to fit a nest if you really need one
a divertor valve controls where hot water from your boiler goes BTW.

I hope you have one or two on your system. if not that explains why you get heating and hot water no matter what you switch on. the valves should prevent the heating circuit getting water when you turn on the hot water and vice versa
topbloke

a divertor valve controls where hot water from your boiler goes BTW.I … a divertor valve controls where hot water from your boiler goes BTW.I hope you have one or two on your system. if not that explains why you get heating and hot water no matter what you switch on. the valves should prevent the heating circuit getting water when you turn on the hot water and vice versa



Thanks for the response! I had a guy come over recently because my programmer stopped supplying power to my central heating pump for some reason - anyway he went looking for a diverter valve and said he couldn't find one! so he just hard wired the "Heating On" behind the programmer to live so at the very least I had heating and water - think im just going to concentrate on getting that sorted first and a new programmer put in and ask the guy about finding and / or fixing the diverter valve!
I'm not a plumber and I'm sure you will get more responses but just find a good tradesman to fix.
Surely if you had no valves regardless of the setting you'd always get the same? I had a similar problem which was a seized three way valve. This device, in my case, is next to the hot water tank.
Jez1970

Surely if you had no valves regardless of the setting you'd always get … Surely if you had no valves regardless of the setting you'd always get the same? I had a similar problem which was a seized three way valve. This device, in my case, is next to the hot water tank.



Well i think its possible i dont have any valves because the way i was getting only hot water and it keeping the central heating off was by the programmer not sending power to the central heating pump when i selected hot water only? whereas when i choose central heating only the pump gets power and i get hot water too because i have no diverter valves? Does that sound like a likely scenario? Just had a neighbour look who also cant find a diverter valve!
You need 2 motorised valves for water and heating to work independently. A job for a heating engineer.
topbloke

if you are getting hot water when you have selected heating only then you … if you are getting hot water when you have selected heating only then you have a problem...either incorrect plumbing or a faulty divertor valve...get that fixed and tell the plumber to fit a nest if you really need one


No they dont' have a problem, that's how their system is supposed to work , Gravity hot water and pumped central heating you can't have heating on its own as the hot water heats up anyway.
Plenty of systems installed that way without motorised valves
Edited by: "souljacker" 13th Feb 2015
As everyone else has said, you need a valve that switches between just hot water, or just heating or both. However, are you sure that the hot water is not just hot from when it was heated up by the timer earlier on in the day? If you have a hot water tank in the airing cupboard, you should get hot water all day long if you have the hot water fire for an hour in the morning and an hour in the evening. Have you tried running a hot bath to clear out the hot water tank and then see if the hot water heats back up if you just turn on the heating?

That aside, Nest will nto have any control over your hot water. What you will do is turn on your heating to 'always on' at your timer. The Nest will then take over the programming duties from your old timer even though that will remain in place. The Nest is a smart thermostat, so can be controlled by an app whilst you are not at home and also learn your routine so your house should always be warm without the need to leave the heating on all day long. You will keep your exisiting programmer as that will need to be used for running your hot water twice a day (or whatever it is you do).

If you have a combi boiler however, water will be heated on demand and will not need a timer. I'm assuming you don't have this as I'm pretty sure you would have mentioned it.
Pretty clear its not a combi boiler as they have said they have a feeder tank in the loft and a water cylinder.
souljacker

No they dont' have a problem, that's how their system is supposed to work … No they dont' have a problem, that's how their system is supposed to work , Gravity hot water and pumped central heating you can't have heating on its own as the hot water heats up anyway.Plenty of systems installed that way without motorised valves



Not true. They may well exist, but it's not how it should work. There should be a motorised valve that works to isolate hot water or heating or both at the same time. I have a gravity fed hot water from a tank and pumped central heating and have the isolator valve. It was installed over 15 years ago and a couple of years ago the valve packed in so that the radiators were heating up when the hot water came on (opposite problem to OP), which was a pain in the summer.

Comment

souljacker

No they dont' have a problem, that's how their system is supposed to work … No they dont' have a problem, that's how their system is supposed to work , Gravity hot water and pumped central heating you can't have heating on its own as the hot water heats up anyway.Plenty of systems installed that way without motorised valves


Mine was exactly the same when we moved in. Then BG said I needed one to carry on having a service contract with them.
So we had one fitted close to the hot water tank. That was 2.5 years ago. Guess what the only thing to break has been? Yep the diverter. Just as well I cancelled BG a year plus ago. Screwfix had the part for £42 and required no plumbing.
souljacker

Pretty clear its not a combi boiler as they have said they have a feeder … Pretty clear its not a combi boiler as they have said they have a feeder tank in the loft and a water cylinder.



Yeah, I added that just in case other people in more modern homes with only combi boilers chipped in.
Oneday77

CommentMine was exactly the same when we moved in. Then BG said I needed … CommentMine was exactly the same when we moved in. Then BG said I needed one to carry on having a service contract with them. So we had one fitted close to the hot water tank. That was 2.5 years ago. Guess what the only thing to break has been? Yep the diverter. Just as well I cancelled BG a year plus ago. Screwfix had the part for £42 and required no plumbing.


Yeah you can usually just change the head on the motorised valves or even the synchron motor inside which is even cheaper
Oneday77

CommentMine was exactly the same when we moved in. Then BG said I needed … CommentMine was exactly the same when we moved in. Then BG said I needed one to carry on having a service contract with them. So we had one fitted close to the hot water tank. That was 2.5 years ago. Guess what the only thing to break has been? Yep the diverter. Just as well I cancelled BG a year plus ago. Screwfix had the part for £42 and required no plumbing.



It will require plumbing if there isn't currently one there or the valve has ceased up. But if it is just the motor that has gone, they just slot in place and just need to be wired back to exactly how the old one was wired (take photos with your phone before you remove any wires just so you can see where they went).
Denziloshamen

Not true. They may well exist, but it's not how it should work. There … Not true. They may well exist, but it's not how it should work. There should be a motorised valve that works to isolate hot water or heating or both at the same time. I have a gravity fed hot water from a tank and pumped central heating and have the isolator valve. It was installed over 15 years ago and a couple of years ago the valve packed in so that the radiators were heating up when the hot water came on (opposite problem to OP), which was a pain in the summer.


Yes it is true, most modern systems do now have motorised valves but a lot of the older ones were just installed with a pump for the heating and the hot water worked on gravity from the boiler stat, now they are fitted with a motorised valve linked to the cylinder stat.
There is no regulation that says you must fit a motorised valve on an older system
souljacker

Yeah you can usually just change the head on the motorised valves or even … Yeah you can usually just change the head on the motorised valves or even the synchron motor inside which is even cheaper


I didn't look as far as doing the motor as I could already get a part that day and £42 in the grand scheme of things involving tradesmen call outs was a bargain.
It also helped me learn something new to boot
You must have one divertor valve.
You should check that the hall thermo stat is controlling boiler and not divertor valve.

Our hall thermostat used to control the divertor , so once the house was upto temp the thermo/divertor would turn to just hot water mode. This was bad as boiler was never really off, now our hall thermostat just controls boiler on off directly in conjuction with a timer.

I looked at the smart thermostats like Nest, but preferd the simpler timer systems with defined on off periods and the option to manually advance to heating, simple and cant go wrong
Edited by: "lumsdot" 13th Feb 2015
Since you cant just get hot radiators only , i think this means you just have one diverter valve. If you have two diverters you can get any combination of hot water / radiators.

If you hall thermo stat is controlling the diverter, you will known because once thermostat clicks off the boiler will still come on occasionally to heat hot water, which is bad as water gets very hot and it uses a lot of gas/oil.

Heating both radiators and hot water at same time, is not a problem for us, as the thermostat on boiler is not turned up high and boiler is not on 24 hours a day. If you have boiler thermo stat set too high then hot water can become scalding

Edited by: "lumsdot" 13th Feb 2015
Denziloshamen

As everyone else has said, you need a valve that switches between just … As everyone else has said, you need a valve that switches between just hot water, or just heating or both. However, are you sure that the hot water is not just hot from when it was heated up by the timer earlier on in the day? If you have a hot water tank in the airing cupboard, you should get hot water all day long if you have the hot water fire for an hour in the morning and an hour in the evening. Have you tried running a hot bath to clear out the hot water tank and then see if the hot water heats back up if you just turn on the heating?That aside, Nest will nto have any control over your hot water. What you will do is turn on your heating to 'always on' at your timer. The Nest will then take over the programming duties from your old timer even though that will remain in place. The Nest is a smart thermostat, so can be controlled by an app whilst you are not at home and also learn your routine so your house should always be warm without the need to leave the heating on all day long. You will keep your exisiting programmer as that will need to be used for running your hot water twice a day (or whatever it is you do).If you have a combi boiler however, water will be heated on demand and will not need a timer. I'm assuming you don't have this as I'm pretty sure you would have mentioned it.



Thanks for the response - the hot water is definately staying on, ive tried clearing the tank and it comes back hot very quick. So with this nest will i have to keep my hot water always on for it to work?
souljacker

Pretty clear its not a combi boiler as they have said they have a feeder … Pretty clear its not a combi boiler as they have said they have a feeder tank in the loft and a water cylinder.



Yeah its defo not a combi boiler - purely gravity based system
Oneday77

CommentMine was exactly the same when we moved in. Then BG said I needed … CommentMine was exactly the same when we moved in. Then BG said I needed one to carry on having a service contract with them. So we had one fitted close to the hot water tank. That was 2.5 years ago. Guess what the only thing to break has been? Yep the diverter. Just as well I cancelled BG a year plus ago. Screwfix had the part for £42 and required no plumbing.



Had what fitted diverter valves? how much did that cost? Also i have noticed there is no thermostat anywhere near my big tank......not sure if thats normal?
sunnygilluk

Had what fitted diverter valves? how much did that cost? Also i have … Had what fitted diverter valves? how much did that cost? Also i have noticed there is no thermostat anywhere near my big tank......not sure if thats normal?


It's normal on older systems, your hot water it running off your boiler stat , if you want to run them individually you would need to fit a diverter valve to the heating and hot water system and have a stat fitted on the cylinder linked to the diverter valve.
Not really worth the cost though, full system drain down, wiring through from cylinder to valve and wiring back to programmer
Edited by: "souljacker" 13th Feb 2015
sunnygilluk

Had what fitted diverter valves? how much did that cost? Also i have … Had what fitted diverter valves? how much did that cost? Also i have noticed there is no thermostat anywhere near my big tank......not sure if thats normal?


I actually stumbled upon the bill tonight, which I'm ashamed to admit how much BG ripped the bum out us. £350 Oo
I'm sure a local plumber would be much cheaper but to be honest with a new baby in the house at the time I had no time or energy to do some digging. Also I was keen to ensure heating would always work.
sunnygilluk

Thanks for the response - the hot water is definately staying on, ive … Thanks for the response - the hot water is definately staying on, ive tried clearing the tank and it comes back hot very quick. So with this nest will i have to keep my hot water always on for it to work?



No. Once you get the issue with your hot water sorted out, then you leave your heating as 'always on' (so the Nest can control it) and your hot water timed as you want it. It sounds as though your heating system needs a few improvements to save you some money in the long run. Your hot water tank should have a little thermostat attached to it so that your water doesn't continually heat up and become too hot. Once the thermostat senses the hot water tank is above a certain temperature (I think mine is set somewhere between 55 and 60 degrees) it will stop the water from heating up any further. It also sounds as though you need a motorised isolator valve fitting so you only have the water heating when you want the water heating. I'm not sure a Nest is going to serve you that well until your system is more efficient.
Its a pretty simple and common set up on older systems, I'd only update it when upgrading the boiler.

It should work like this:

Hot water - boiler on, gravity circulation heats up cylinder.
Heating - boiler on, pump on, heating comes on, cylinder heats through gravity still.

If you want to fit nest just replace the thermostat with nest, in this instance it will be controlling the pump (and maybe the boiler on/off depending on wiring).
Denziloshamen

No. Once you get the issue with your hot water sorted out, then you leave … No. Once you get the issue with your hot water sorted out, then you leave your heating as 'always on' (so the Nest can control it) and your hot water timed as you want it. It sounds as though your heating system needs a few improvements to save you some money in the long run. Your hot water tank should have a little thermostat attached to it so that your water doesn't continually heat up and become too hot. Once the thermostat senses the hot water tank is above a certain temperature (I think mine is set somewhere between 55 and 60 degrees) it will stop the water from heating up any further. It also sounds as though you need a motorised isolator valve fitting so you only have the water heating when you want the water heating. I'm not sure a Nest is going to serve you that well until your system is more efficient.



Ive tried looking for that thermostat on the tank and cant see one on there either! its usually clipped on to the tank right? from the google pics i can see.
themorgatron

Its a pretty simple and common set up on older systems, I'd only update … Its a pretty simple and common set up on older systems, I'd only update it when upgrading the boiler.It should work like this:Hot water - boiler on, gravity circulation heats up cylinder.Heating - boiler on, pump on, heating comes on, cylinder heats through gravity still.If you want to fit nest just replace the thermostat with nest, in this instance it will be controlling the pump (and maybe the boiler on/off depending on wiring).



Ok thanks for the reply, so to sum it up, for NEST i have to leave central heating to always on - which in my system means hot water must also be on.

So does that mean hot water is also always on if i install a NEST? and the nest just controls the central heating pump to get the house hotter? or is it more intelligent and will actually switch my hot water and central heating off by turning off the pump and boiler? (unless the hot water settings on the programmer override it)
Edited by: "sunnygilluk" 14th Feb 2015
sunnygilluk

Ok thanks for the reply, so to sum it up, for NEST i have to leave … Ok thanks for the reply, so to sum it up, for NEST i have to leave central heating to always on - which in my system means hot water must also be on.So does that mean hot water is also always on if i install a NEST? and the nest just controls the central heating pump to get the house hotter? or is it more intelligent and will actually switch my hot water and central heating off by turning off the pump and boiler? (unless the hot water settings on the programmer override it)



Nest will not be able to switch hot water on/off, if you have heating on hot water will always be heated. Nest can only control a single 'channel' (normally heating).

If you install a nest thermostat I would expect to be able to turn heating on/off (meaning switching pump on/off, but usually its wired to also switch boiler on/off). You will still need to control hot water via the traditional programmer. If you have heating on hot water will be heated regardless - to alter this could be a big expense.

There's quite a few variables with an older system, the other thing to consider is assuming you have a hot water cylinder stat this will also stop the boiler firing when the water is hot enough.
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