U
undertrained
Just making assumptions based on what I remember from Honeywell training (approx 8 years ago) , in on 1 out on 3.
Changing a Thermostat stuck with wiring
- Thread starter smon jones
- Start date
Just making assumptions based on what I remember from Honeywell training (approx 8 years ago) , in on 1 out on 3.
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since the introduction of the industry standard backplates the wiring is supposed to be unified, as you say for single channel heating it would be 1 and 3 but with so many chinese and other countries flooding the market thy dont always follow the same wiring as us
not to mention Hive's compromised design of a receiver that was "plug compatible" with "unified" wiring
The Single Channel version has potential free contacts, can be used for 230 volt or 24 volt switching.
The Dual Channel vereion has the two switches internally connected to Live 230 volt,
The reason behind that is the single channel switches the boiler so has to be voltage free switching to suit all boilers, the dual channel will be switchin a 3 way or 2 x 2 port valves which always require 240v , it is the motorised valves that switch the boiler not the hive
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That is good.............all boilers
that is true for MOST systems.
Hive decided to make a pin for pin compatible interface with programmers such as the ST9400 series for the commercial advantage that little if any changes to the wiring would be necessary. Hence easier to sell.
Had Hive gone for a connector with 6 switch terminals then the commons would not have to be tied to Live inside the Hive .
But then with 6 volt free terminals if the Hive was replacing a "standard" programmer with only 4 switch terminals then the installer would have to add wires to link the two switch commons to Live and move existing wires to different terminals.
NO it is true for all Domestic systems
The purpose of the blue (neutral) is to reduce the hysteresis (the difference between the on and off) switching of the stat. It powered a tiny heating element, to improve the reaction delay to old mechanical stats, to temperatures rising. With modern none bi-metal sensors used in modern system like the wireless ones, they can adjust the hysteresis to what ever they like, from no hysteresis to what ever number of degrees might suit the application.
All such systems have to have some hysteresis otherwise your heating system would be switching on and off far too frequently.
All such systems have to have some hysteresis otherwise your heating system would be switching on and off far too frequently.
It gets complicated. In olden days the heater did as you say, but now it is said that with boilers that do not modulate the thermostat should be switching the boiler off before the room reaches the desired temperature to avoid overshooting the required temperature. There is a thread about this with a graph of the boiler being turned on and off.
W Plan system as well ?
That is exactly what the tiny heating element in the thermostat does, it turns the heating system off, before it attains the set temperature.
For instance..
Designed hysteresis is 1.5C; stat is set to 20C on the dial - actual temperature falls to <18.5C, thermostat switch on, heating switches on, heating element in stat is switched on. Bi-metal stat receives heat from heating system and from its heating element, therefore switches off. Bi-metal without the element, would maybe switch on at 18.5C, but not click open until maybe 22C.
why would anyone want to use a Hive with a W plan ?
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The Y plan and W plan are very similar except no centre position. However you can get 24 volt motorised valves and 24 volt boilers not sure about pumps, so if the programmer can only switch 230 volt clearly it limits the systems it can work with, also many systems used the programmer as a junction box, and the small terminals used in the likes of Nest mean you have to have a wiring centre added to accommodated the more than two wires in a terminal.
I am sure Nest will work with 90% of domestic central heating systems and Hive likely 70% but due to some manufacturers refusing to standardise, with the likes of the new Worcester Bosch it will only work in modulating mode with their own thermostat, and since the thermostat does no link to the TRV heads it is rather limited on how it can work efficiently.
Most will still work by switching on/off, and I am not sure how much is gained or lost modulating a boiler rather that switching off/on, it depends so much on boiler design, theory is great, the idea is the liquid is cool before the boiler switches off/on to control so on switching off very little energy is lost up the flue, where if it is not allowed to modulate each time it switches off far more energy is lost through the flue as it is running hotter.
However that assumes the boiler runs at same or better efficiency as the output decreases.
In my new house I have oil, the boiler will modulate, from 24 kW to 18 kW I really don't know why they bothered making it modulate? and since the domestic hot water is thermo syphon after it turns off, the heat can still go into domestic hot water it does not have to go out the flue.
With a boiler that modulates from 28 kW to 6 kW yes it can work, but at even 6 kW at 3p per kWh that's £1567 per year or £4.32 per day. I would guess 4 months the system is turned off, and 4 months over 6 kW is used so for half the time the boiler is used it can't modulate low enough so it uses the mark/space anyway.
Before moving I was on gas, and I set the TRV so the boiler should modulate rather than switch off on the wall thermostat, hall TRV set at 18°C and thermostat on wall in hall set to 19°C so in theory the boiler should not turn off but modulate, however it did turn off, so either the 8 kW was too much for house, or the thermostat was switching off early.
Theory one should not need a wall thermostat, the TRV should control each room and the boiler modulate according to return water temperature, but in practice it does not work, just spent ages fitting a wall thermostat with motorised valves as when using boiler for domestic hot water, the radiators still got hot, OK the electronic TRV heads switched fully off, but the old wax type did not.
I am sure Nest will work with 90% of domestic central heating systems and Hive likely 70% but due to some manufacturers refusing to standardise, with the likes of the new Worcester Bosch it will only work in modulating mode with their own thermostat, and since the thermostat does no link to the TRV heads it is rather limited on how it can work efficiently.
Most will still work by switching on/off, and I am not sure how much is gained or lost modulating a boiler rather that switching off/on, it depends so much on boiler design, theory is great, the idea is the liquid is cool before the boiler switches off/on to control so on switching off very little energy is lost up the flue, where if it is not allowed to modulate each time it switches off far more energy is lost through the flue as it is running hotter.
However that assumes the boiler runs at same or better efficiency as the output decreases.
In my new house I have oil, the boiler will modulate, from 24 kW to 18 kW I really don't know why they bothered making it modulate? and since the domestic hot water is thermo syphon after it turns off, the heat can still go into domestic hot water it does not have to go out the flue.
With a boiler that modulates from 28 kW to 6 kW yes it can work, but at even 6 kW at 3p per kWh that's £1567 per year or £4.32 per day. I would guess 4 months the system is turned off, and 4 months over 6 kW is used so for half the time the boiler is used it can't modulate low enough so it uses the mark/space anyway.
Before moving I was on gas, and I set the TRV so the boiler should modulate rather than switch off on the wall thermostat, hall TRV set at 18°C and thermostat on wall in hall set to 19°C so in theory the boiler should not turn off but modulate, however it did turn off, so either the 8 kW was too much for house, or the thermostat was switching off early.
Theory one should not need a wall thermostat, the TRV should control each room and the boiler modulate according to return water temperature, but in practice it does not work, just spent ages fitting a wall thermostat with motorised valves as when using boiler for domestic hot water, the radiators still got hot, OK the electronic TRV heads switched fully off, but the old wax type did not.
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