Replacing a heating thermostat
- Thread starter LfcDom11
- Start date
Sponsored Links
- Joined
- 17 Aug 2010
- Messages
- 2,746
- Reaction score
- 453
- Country
Didn't it come with instructions - and a type number?
You do not need the earth so just put a connector block on it and position safely out of the way.
You have a Neutral terminal on the new one - this may make it work better but may not actually be essential.
What is the model number of the thermostat?
You have a Neutral terminal on the new one - this may make it work better but may not actually be essential.
What is the model number of the thermostat?
Sponsored Links
http://www.tfc-group.co.uk/assets/graphics/static/STTRSA.pdf
There you go - connect to 1 and 2
Says neutral not required. Why has it got a terminal, then?
There you go - connect to 1 and 2
Says neutral not required. Why has it got a terminal, then?
Attachments
Don't know why the attached file has appeared.
Does anyone know how to get rid of it; it doesn't appear in the Edit.
Does anyone know how to get rid of it; it doesn't appear in the Edit.
- Joined
- 17 Aug 2010
- Messages
- 2,746
- Reaction score
- 453
- Country
The wires you have are live (1) and switched live (2). If it were neutral there'd be a big bang.
And yes, earth in a terminal block.
And yes, earth in a terminal block.
A lot of them have the wiring diagram printed on the inside of the lid.
- Joined
- 27 Jan 2008
- Messages
- 23,733
- Reaction score
- 2,675
- Location
- Llanfair Caereinion, Nr Welshpool
- Country
Although with new thermostat neither earth or neutral are required and one would simply connect the two wires, with the old one neutral was likely required and it seems likely the wire coloured as earth is actually a neutral.
It does not matter now, but could matter in the future if the thermostat is changed again.
It does not matter now, but could matter in the future if the thermostat is changed again.
It might be an Earth used as a "neutral" to supply the accelerator resistor. This is NOT good practice but allows the bodger to use twin and earth instead of bothering with triple and earth. The current through the accelerator resistor is often small wnough that an RCD on the will not be tripped by it.
accelerator resistor = a small resistor that creates heat in the thermostat to reduce the difference between the air temperatures at which the bi-metallic strip switches ON and OFF.
- Joined
- 27 Jan 2008
- Messages
- 23,733
- Reaction score
- 2,675
- Location
- Llanfair Caereinion, Nr Welshpool
- Country
I would agree, I have seen so many where the neutral is not connected at all, the differential can be a couple of degrees without that wire, using batteries to power the thermostat is also quite common, mine is battery powered and has a clock built in so changes the temperature set depending on time, rather than using the old time clock which simply turned off the central heating at night.
But when I fitted a free standing wireless thermostat in my mother house I realised it is where it is that matters more than the differential setting, it seemed wrong but putting it close to the radiator worked better than keeping it away from radiators, doors and windows. Once I realised it was better close to radiator it made a huge difference to comfort. I had to of course compensate for it being close, setting to 22°C instead of 19°C but it then kept room at 18.5 to 19°C when away from the radiator it was 19 to 24°C as it took so long for the heat to reach the thermostat by which time the area near to radiator was far too hot.
It seems we are taught how the electric bit works, but not how heat travels or more to the point does not travel through the room. The same was true with open fires, today I realise for a open flue fire to work it need the combustion air to be local supplied to it. With a vent or duct near the fire it heated without drafts, but without that air supply there is a draft under every door.
As we went to balanced flue we started to block up the fresh air vents and get better fitting doors but this in turn has messed up the control because the air does not move.
I found this out brewing beer, on heating in a freezer it would over shoot but on cooling it did not, main reason was on cooling there is a fan running. As to if having a fan running in the room would help keep the room at a steady temperature I don't know? I have a Myson which seems to make it worse not better, but that is likely down to having no store of hot water, the radiator stays hot even when the heating turns off. But the Myson cools down in minutes once the flow of water stops.
But when I fitted a free standing wireless thermostat in my mother house I realised it is where it is that matters more than the differential setting, it seemed wrong but putting it close to the radiator worked better than keeping it away from radiators, doors and windows. Once I realised it was better close to radiator it made a huge difference to comfort. I had to of course compensate for it being close, setting to 22°C instead of 19°C but it then kept room at 18.5 to 19°C when away from the radiator it was 19 to 24°C as it took so long for the heat to reach the thermostat by which time the area near to radiator was far too hot.
It seems we are taught how the electric bit works, but not how heat travels or more to the point does not travel through the room. The same was true with open fires, today I realise for a open flue fire to work it need the combustion air to be local supplied to it. With a vent or duct near the fire it heated without drafts, but without that air supply there is a draft under every door.
As we went to balanced flue we started to block up the fresh air vents and get better fitting doors but this in turn has messed up the control because the air does not move.
I found this out brewing beer, on heating in a freezer it would over shoot but on cooling it did not, main reason was on cooling there is a fan running. As to if having a fan running in the room would help keep the room at a steady temperature I don't know? I have a Myson which seems to make it worse not better, but that is likely down to having no store of hot water, the radiator stays hot even when the heating turns off. But the Myson cools down in minutes once the flow of water stops.
I think there is something is seriously wrong with your existing installation!
The old thermostat looks like a Satchwell Sunvic TLX to me, there are lots of variants out there but I believe it maybe a model 2259, The model number and a wiring diagram should be shown in the lid, or on the terminal cover. If it is a different model, then the following may not apply, so it is crucial that you find out what you actually have. If it is a 2259 then:-
It should be a four wire installation, the earth connection should be made to an earth terminal on a metal backplate behind what is shown in your photograph. [see image below which should have an earth sleeve but was the only picture I could find] My guess is that there is not an earth wire connected to yours, and so in the event of a fault, you may have a potentially dangerous installation.
The thermostat is then screwed to this backplate and the three terminals numbered left to right are 1, 3 & 4. [Terminal 2 is for cooling applications and not fitted to this model]
Terminal 1 is the switched live that leaves the thermostat to control the heating
Terminal 3 is the live supply to the thermostat
Terminal 4 Should be a neutral to operate the 'accelerator' (it seems like the earth wire has been used for this function and even wrongly identified as an earth by fitting an earth sleeve, on the other hand if it really is connected to earth at the other end, it should not be connected to that terminal)
The remedy is to remove the existing 2 core and earth cable and install a three core and earth, or install a thermostat that doesn't need a neutral connection.
The new thermostat you show looks like a Honeywell, you can download an installation guide here. Unfortunately, they do normally need a Neutral connection to work effectively.
The old thermostat looks like a Satchwell Sunvic TLX to me, there are lots of variants out there but I believe it maybe a model 2259, The model number and a wiring diagram should be shown in the lid, or on the terminal cover. If it is a different model, then the following may not apply, so it is crucial that you find out what you actually have. If it is a 2259 then:-
It should be a four wire installation, the earth connection should be made to an earth terminal on a metal backplate behind what is shown in your photograph. [see image below which should have an earth sleeve but was the only picture I could find] My guess is that there is not an earth wire connected to yours, and so in the event of a fault, you may have a potentially dangerous installation.
The thermostat is then screwed to this backplate and the three terminals numbered left to right are 1, 3 & 4. [Terminal 2 is for cooling applications and not fitted to this model]
Terminal 1 is the switched live that leaves the thermostat to control the heating
Terminal 3 is the live supply to the thermostat
Terminal 4 Should be a neutral to operate the 'accelerator' (it seems like the earth wire has been used for this function and even wrongly identified as an earth by fitting an earth sleeve, on the other hand if it really is connected to earth at the other end, it should not be connected to that terminal)
The remedy is to remove the existing 2 core and earth cable and install a three core and earth, or install a thermostat that doesn't need a neutral connection.
The new thermostat you show looks like a Honeywell, you can download an installation guide here. Unfortunately, they do normally need a Neutral connection to work effectively.
Last edited:
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
Sponsored Links
