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Replacing a thermostat

Does what it says on the tin
paulnumbers
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Replacing a thermostat

#250701

Postby paulnumbers » September 10th, 2019, 11:20 am

Wonder if anyone can recommend a way forward.

I have a combi boiler in the loft, vokera 29e, and this has a 24 hour rotary timer on it, (ie, not 7 days, or programmable).

Connected in the living room is a very old style thermostat. It has 4 wires as seen in the following pictures (should be 4 pictures on this link)

https://imgur.com/a/qWky58B

As I can only control the timing from the loft, I want to change the system slightly. Seems like I have 2 broad options.

1) new wizz bang smart system like honeywell evohome - total cost about £600

2) swap out the thermostat with a programmable one, something like honeywell t4h110a1021 - cost about £60

As can be seen, thermostat has 4 cables, earth, break on temp rise, spare terminal, common. I’m a little confused by the blue wire on the spare terminal, as in the loft only 3 wires arrive (on the left hand side of the wiring picture). Is it possible that the thermostat also takes power directly from a separate mains feed, rather than the boiler?

There is 240v between earth & “break on temp rise”.

So, my question is, does it make sense to replace the thermostat with a basic programmable 230v thermostat, and then turn the boiler to “on 24 hours”?

The evohome system seems tempting, but will require me to get a plug socket installed in the loft, not the end of the world I guess. Ultimately I want to be able to set the heating to come on/off at different times depending on the day. Long term it would be be nice to go down the whole evohome setup, where you can control room temp individually with digital trv’s

Appreciate any thoughts, apologies that it’s all a bit rambling.

Paul

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Re: Replacing a thermostat

#250729

Postby pendas » September 10th, 2019, 1:01 pm

So, my question is, does it make sense to replace the thermostat with a basic programmable 230v thermostat, and then turn the boiler to “on 24 hours”?


It makes sense to me. Since I fitted a programmable thermostat the boiler is set to 24 hours on and the programmed temperature and actual hall temperature determine if and when the boiler fires. Overnight the temperature is set at a level that the house rarely falls to.

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Re: Replacing a thermostat

#250740

Postby staffordian » September 10th, 2019, 1:43 pm

I swapped a similar old style thermostat a couple of years ago, fitting a Salus RT510 which cost around £30. I suspect the Honeywell you refer to does a similar job.

Most of these are actually battery operated as far as powering it and doing the actual switching is concerned, and only use (IIRC) two wires, rather than the three or four in old thermostats. YouTube etc give details, as, of course, would the fitting instructions.

As you say, the existing programmer is set to 24hrs and all control taken by the programmable stat. To switch the heating off, eg overnight, simply set the stat to 15C or whatever figure is low enough to prevent the stat calling for heat.

Fitting this has transformed our system from a clunky either too hot or too cold system to one I can rely on to keep us comfortable. I can't recommend it highly enough.

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Re: Replacing a thermostat

#250756

Postby DrFfybes » September 10th, 2019, 2:40 pm

paulnumbers wrote:
So, my question is, does it make sense to replace the thermostat with a basic programmable 230v thermostat, and then turn the boiler to “on 24 hours”?

Paul



Yes.

Alternatively replace the current Stat with a reciver and fit a wireless stat in a different room if required (fitting the receiver in the loft on the boiler cant lead to poor siglan).

Paul

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Re: Replacing a thermostat

#250759

Postby pochisoldi » September 10th, 2019, 2:53 pm

paulnumbers wrote:As can be seen, thermostat has 4 cables, earth, break on temp rise, spare terminal, common. I’m a little confused by the blue wire on the spare terminal, as in the loft only 3 wires arrive (on the left hand side of the wiring picture). Is it possible that the thermostat also takes power directly from a separate mains feed, rather than the boiler?


Most likely that the cable was installed years ago, and isn't connected, or it's connected to neutral at the boiler,
Some old school thermostats have 4 wires - live, switched live, earth, and a neutral which connects to an "accelerator resistor".

This makes the thermostat get up to temperature more quickly, resulting in the boiler cycling on and off.
The idea was to have the boiler cycle on and off and slowly get to the desired set point, rather than having the boiler on all the time, and then overshooting the target in the room with the thermostat, whilst other rooms struggle to get up to temperature.

You almost certainly don't need it. Treat it as live - secure the wire in a single choc block and insulate.

So, my question is, does it make sense to replace the thermostat with a basic programmable 230v thermostat, and then turn the boiler to “on 24 hours”?


Most (if not all) programmable stats are battery powered, with volt free contacts, so you just move the two wires that were connected to the mechanical thermostat contacts onto the corresponding common and call for heat terminals on the programmable stat, fasten the earth wire to the backbox, secure and insulate the 4th wire.

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Re: Replacing a thermostat

#250778

Postby Itsallaguess » September 10th, 2019, 3:59 pm

staffordian wrote:
I swapped a similar old style thermostat a couple of years ago, fitting a Salus RT510 which cost around £30. I suspect the Honeywell you refer to does a similar job.

Most of these are actually battery operated as far as powering it and doing the actual switching is concerned, and only use (IIRC) two wires, rather than the three or four in old thermostats. YouTube etc give details, as, of course, would the fitting instructions.

As you say, the existing programmer is set to 24hrs and all control taken by the programmable stat. To switch the heating off, eg overnight, simply set the stat to 15C or whatever figure is low enough to prevent the stat calling for heat.

Fitting this has transformed our system from a clunky either too hot or too cold system to one I can rely on to keep us comfortable. I can't recommend it highly enough.


Another Salus fan here, although I installed one of the wireless thermostat units, and like you I've found that comfort levels rose dramatically with an improved set of granular controls for heating times etc.

I note that the Salus RT510RF, which is a newer model than the one I've installed, is currently on offer from Amazon for £36 delivered -

https://www.amazon.co.uk/Salus-RT510RF- ... B072KL746L

Regarding wireless signal strength, our boiler and receiver is in a bathroom cupboard upstairs, and I have no issues with the wireless unit being on the lower floor. A loft-mounted receiver would need to be tested for suitability, I'd imagine.

Let's also not forget that whilst units like this provide timing and 'desired room-temperature' controls, there are also two other separate heating controls in most modern central-heating installations -

1. Local Thermostatic Radiator Valve (TRV) control on individual radiators

2. 'Return temperature' heating control on the boiler itself.

So including the temperature setting on any external-thermostat itself, all three sets of temperature settings will normally need careful calibration to achieve the spread of heating levels required throughout a home.

As an aside, we tend to prefer a colder bedroom at night, so I installed an electronic TRV on our bedroom radiator that allows us to set that TRV to close down completely earlier in the evening, without any further manual intervention, and then re-open for normal use the next morning. After a quick look online there now seems to be a huge range of Alexa / Google Home TRV's on the market now too, but I think they are both expensive and overcomplicated for what it often just a requirement for individual timing applications for some radiator TRV's, so our much simpler timer-only version is ideal for what we're wanting.

Cheers,

Itsallaguess

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Re: Replacing a thermostat

#250794

Postby MyNameIsUrl » September 10th, 2019, 4:40 pm

Itsallaguess wrote: ...so I installed an electronic TRV on our bedroom radiator that allows us to set that TRV to close down completely earlier in the evening, without any further manual intervention, and then re-open for normal use the next morning.

Hope you don't mind me asking, but it it noisy when it re-opens in the morning? What make did you use - presumably it's just a head swap, no need to break into the water circuit?

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Re: Replacing a thermostat

#250807

Postby Itsallaguess » September 10th, 2019, 5:24 pm

MyNameIsUrl wrote:
Itsallaguess wrote:
...so I installed an electronic TRV on our bedroom radiator that allows us to set that TRV to close down completely earlier in the evening, without any further manual intervention, and then re-open for normal use the next morning.


Hope you don't mind me asking, but it it noisy when it re-opens in the morning? What make did you use - presumably it's just a head swap, no need to break into the water circuit?


No problem at all, and it's something that needed some consideration for me too, as I'm a very light sleeper and a noisy electronic TRV opening up in the morning is likely to cause me issues, so I solved the problem using the normal operation of the central-heating timings -

1. Normal day-time operation - Central heating is on and the electronic TRV in the bedroom is 'open'
2. 5pm - Bedroom electronic-TRV closes whilst the rest of central heating is still on - resulting in a cooler bedroom at night with no manual intervention..
3. 8.30pm - Central heating turns off completely via Salus wireless thermostat timer
4. 9pm - Bedroom TRV opens up for 'normal operation', which whirs the TRV for around 45 seconds but this isn't a problem because we're still up at this time - Note that the central heating is still off at this time, so no heat is delivered to the bedroom radiator...
5. 5.45am - Central heating turns on fully again, providing heat to all radiators including the bedroom one...
6. Repeat....

Regarding the one I installed, it was this one, although I note that it doesn't seem to be available new from Amazon via this link -

https://www.amazon.co.uk/Homexpert-Heat ... B007AQ71U4

There are many other newer makes and models available, although as I said earlier they seem to be adding more and more expensive bells and whistles such as bluetooth and Alexa/Google Home compatibility - we just needed a normal TRV operation with an individual timing functionality, and if you have a search around for 'electronic TRV' then there still seems to be plenty of cheap options available amongst the glitteringly expensive ones...

Cheers,

Itsallaguess

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Re: Replacing a thermostat

#250816

Postby paulnumbers » September 10th, 2019, 6:31 pm

Thank you very much all, particularly to pochisoldi with the helpful instructions on the cabling.

I've decided I'll grab myself a Salus RT510, the hard wired version, and get that setup in the next few days. I also like the idea of getting hold of a couple of digital TRV's for some rooms where it would be useful to turn the heating off at certain times of the day, without going the more expensive EVOhome full solution. I'll do a little research into this.

Thanks again.

Paul

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Re: Replacing a thermostat

#250823

Postby AF62 » September 10th, 2019, 6:59 pm

paulnumbers wrote:1) new wizz bang smart system like honeywell evohome - total cost about £600

2) swap out the thermostat with a programmable one, something like honeywell t4h110a1021 - cost about £60


Why not half-way house with something like a Nest or Hive? Hive is around £190 installed or £130 self-install, but with Black Friday approaching there are bound to be some deals.

A happy Hive user myself, having changed from a Honeywell programmable thermostat a couple of years ago. The programmable thermostat was FAR better than the dial on the wall, but a smart thermostat like Hive takes it to the next level. Simple things like turning the heating up if you are coming home early or turning it down if you are unexpectedly late. And the ultimate luxury of turning the thermostat up, which is downstairs, whilst still in bed upstairs.

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Re: Replacing a thermostat

#250825

Postby Lootman » September 10th, 2019, 7:09 pm

AF62 wrote:Why not half-way house with something like a Nest or Hive? Hive is around £190 installed or £130 self-install, but with Black Friday approaching there are bound to be some deals.

A happy Hive user myself, having changed from a Honeywell programmable thermostat a couple of years ago. The programmable thermostat was FAR better than the dial on the wall, but a smart thermostat like Hive takes it to the next level. Simple things like turning the heating up if you are coming home early or turning it down if you are unexpectedly late. And the ultimate luxury of turning the thermostat up, which is downstairs, whilst still in bed upstairs.

Yep, we have a Nest and it's definitely a step further, not to mention that it looks very slick.

Ours is powered off the furnace and so doesn't need batteries. It keeps date and time automatically of course. And responds to movement in the house and manual control, as well as being phone-enabled.

My only worry is that it is owned by Google which already knows a lot about me, and now knows how warm I like my house at different times.

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Re: Replacing a thermostat

#250870

Postby paulnumbers » September 10th, 2019, 10:43 pm

AF62 wrote:
paulnumbers wrote:1) new wizz bang smart system like honeywell evohome - total cost about £600

2) swap out the thermostat with a programmable one, something like honeywell t4h110a1021 - cost about £60


Why not half-way house with something like a Nest or Hive? Hive is around £190 installed or £130 self-install, but with Black Friday approaching there are bound to be some deals.

A happy Hive user myself, having changed from a Honeywell programmable thermostat a couple of years ago. The programmable thermostat was FAR better than the dial on the wall, but a smart thermostat like Hive takes it to the next level. Simple things like turning the heating up if you are coming home early or turning it down if you are unexpectedly late. And the ultimate luxury of turning the thermostat up, which is downstairs, whilst still in bed upstairs.


Yes I considered those too, but for various reasons I was put off them. I guess I'm happy to go for a cheap a dirty solution that fixes 95% of my problems and perhaps think about a more expensive solution after I've seen how it works through the winter. Thanks for the suggestions.

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Re: Replacing a thermostat

#251681

Postby paulnumbers » September 13th, 2019, 6:48 pm

Out with the old - https://i.imgur.com/IqzITxz.png

And in with the new - https://i.imgur.com/4CSW9oD.jpg

Thanks all!

Paul

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Re: Replacing a thermostat

#251844

Postby staffordian » September 14th, 2019, 4:53 pm

paulnumbers wrote:Out with the old - https://i.imgur.com/IqzITxz.png

And in with the new - https://i.imgur.com/4CSW9oD.jpg

Thanks all!

Paul

I hope your are as happy with it as I am. It's pretty intuitive to set up and use, but if you have any questions, post here and I'll try to answer them.

One useful facility in the colder weather is the temporary overide, which can be used to switch the heating off for a while without affecting the programmed settings if you are going out. Eg if you want it off for three hours just press the +Hr button three times then the down arrow a few times to reduce the set point a few degrees. It will go off immediately and return to program three hours later.

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Re: Replacing a thermostat

#252057

Postby paulnumbers » September 15th, 2019, 7:30 pm

staffordian wrote:
paulnumbers wrote:Out with the old - https://i.imgur.com/IqzITxz.png

And in with the new - https://i.imgur.com/4CSW9oD.jpg

Thanks all!

Paul

I hope your are as happy with it as I am. It's pretty intuitive to set up and use, but if you have any questions, post here and I'll try to answer them.

One useful facility in the colder weather is the temporary overide, which can be used to switch the heating off for a while without affecting the programmed settings if you are going out. Eg if you want it off for three hours just press the +Hr button three times then the down arrow a few times to reduce the set point a few degrees. It will go off immediately and return to program three hours later.


I must admit that function did have me a little confused, so thanks for that.

It does seem to lack a simple, one press, “move to next schedule” from what I can tell, but not the end of the world. it’s at least 100 times better than what I had!

Thanks for the recommendation

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Re: Replacing a thermostat

#252060

Postby staffordian » September 15th, 2019, 7:52 pm

paulnumbers wrote:It does seem to lack a simple, one press, “move to next schedule” from what I can tell, but not the end of the world. it’s at least 100 times better than what I had!

Yes, I think you're right that this isn't a feature. If you want to switch it to the next schedule, I think what I would do is simply press the up or down arrow until the set point is at the required figure, which temporarily overrides the programmed temperature until the next scheduled change, effectively doing what you want, as long as you know the figure the next schedule is set for...

And whilst I think about it, one setting you can change (via a DIP switch on the rear of the unit IIRC*) is whether the unit displays in increments of 0.1 or 0.5 degrees. I tried the 0.1option but it is a pain, as you need to press the up and down arrows so many times to change a setting by a degree or two so I have mine displaying in 0.5 degree increments. I dont know if it has an actual effect on the operation of the thermostat, but I certainly haven't noticed any lack of sensitivity by having it set in this way.

*Edit, not a DIP switch, it's the installers menu accessed by pressing three buttons for a few seconds.

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Re: Replacing a thermostat

#252085

Postby bionichamster » September 15th, 2019, 10:30 pm

staffordian wrote:I swapped a similar old style thermostat a couple of years ago, fitting a Salus RT510 which cost around £30. I suspect the Honeywell you refer to does a similar job.
Y
Most of these are actually battery operated as far as powering it and doing the actual switching is concerned, and only use (IIRC) two wires, rather than the three or four in old thermostats. YouTube etc give details, as, of course, would the fitting instructions.

As you say, the existing programmer is set to 24hrs and all control taken by the programmable stat. To switch the heating off, eg overnight, simply set the stat to 15C or whatever figure is low enough to prevent the stat calling for heat.

Fitting this has transformed our system from a clunky either too hot or too cold system to one I can rely on to keep us comfortable. I can't recommend it highly enough.


I too went down the Salus route, no problems, works well.

Bh


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