Just putting a nest into my system. And was wondering if (lr) demand. on my boiler needs connecting. I have connected the nest as per manual. And heating is coming on when needed just testing though and boost is not working for hw. I have schematics for all parts of the system if it's any help to anyone. Also my 3way valve has a loose moving handle from experience with these I thought there usual operation is with slight resistance.
Greenstar ri on y plan ....nest Nest
- Thread starter Connor.b
- Start date
If you are fitting a Nest thermostat to an existing Y-Plan, then no wiring changes are required at the boiler. [Assuming the Y-Plan was correctly working in the first place]
With a Y-Plan; the motorised valve and hot water cylinder thermostat control the boiler, and that will not change when you install Nest. The Nest only controls the power to the hot water cylinder thermostat and motorised valve. Not to the boiler itself.
If the hot water cylinder has already heated up to the temperature set on the cylinder thermostat, then the boiler won't fire up when the boost is selected.
The motorised valve manual lever will have a different resistance depending on its position. There will be resistance from the start when moving it from auto to manual, when it is in the hot water only position, but it will be loose when it is in the heating only position.
With a Y-Plan; the motorised valve and hot water cylinder thermostat control the boiler, and that will not change when you install Nest. The Nest only controls the power to the hot water cylinder thermostat and motorised valve. Not to the boiler itself.
If the hot water cylinder has already heated up to the temperature set on the cylinder thermostat, then the boiler won't fire up when the boost is selected.
The motorised valve manual lever will have a different resistance depending on its position. There will be resistance from the start when moving it from auto to manual, when it is in the hot water only position, but it will be loose when it is in the heating only position.
The above must be the worst explanation written on the working principal of a sundial Y plan system.
That's probably because it's not intended to be an explanation of a Y Plan. 
It's there to help the op understand that the Nest isn't wired directly to the boiler, and explain what it is actually connected to.
It's there to help the op understand that the Nest isn't wired directly to the boiler, and explain what it is actually connected to.
Although the OP didn’t ask for an explanation on the working principal of the Y plan/Nest.That's probably because it's not intended to be an explanation of a Y Plan.
Does the principal of the Sundial Y plan change when installing the Nest/Hive?