Honeywell Sundial Plan Wiring Centre - Permanent Live - Nest

[stem]

As Nest takes care of both the time and temperature control functions, no room thermostat is required. However, if you don't insert a link to join together the 'Live' and 'Switched Live' room thermostat terminals at the wiring centre, the wiring will be permanently 'open circuit' and the central heating won't operate.

I can't remember for sure which two terminals from the block below they are....

....but the diagram / nomenclature inside the lid of the wiring centre should tell you. I think from memory that it's 1 & 3, but make sure you check first.

EDIT:
There you go, it is 1 & 3.

 

[Ray1000]

Thank you very much Stem, I installed a Nest at my son’s house yesterday, he rang last night to say while the hot water was working the heating wasn’t.

I had removed all 4 wires not knowing about the need for a link between 1 and 3

I’m going down shortly to rectify it, I’ll let you know how I go on

Ray

 

[Ray1000]

Having fitted the link between terminals 1 and 3 on the Room Stat connector block the boiler strikes up when the central heating is called for.



Thank you again,
Ray

Also see next post

 

[Ray1000]

Having rectified the missing link on the Room Stat connector block and tested the boiler this afternoon it seemed to being doing as it should. CH and Hot Water starting and stopping with the Nest dial and the App.

This evening I'm being told the boiler appears to be running with the picture of a flame showing even though neither heating or hot water are being called for. I need to explore this tomorrow ... in the meantime the boiler has been turned off.

I need to post a picture of the way the fused spur is wired up as there is an element of this I don't understand ... possibly a frost device which I don't have on the boiler at our house.

 

[CBW]

This evening I'm being told the boiler appears to be running with the picture of a flame showing even though neither heating or hot water are being called for. I need to explore this tomorrow ... in the meantime the boiler has been turned off.

Could be a failed motorised valve.

 

[Ray1000]

Thank you Chris, are you saying a failed motorised valve could cause the flame to show and the internal fan to run when nothing is being called for?

In either event it is one of the things I'll check when I go to the house tomorrow.

 

[Ray1000]

I need to post a picture of the way the fused spur is wired up as there is an element of this I don't understand ... possibly a frost device which I don't have on the boiler at our house.

Would it be better to remove the ancient frost stat as the Nest seems to have that covered?

 

[stem]

A frost stat is normally located in an area where there is a risk of the pipes associated with the heating system freezing, such as unheated outhouse or garage. When the temperature in that area drops to a level where freezing may occur it overrides all of the usual controls and starts the heating. Nest doesn't have a remote sensor that can be located in such an area, so in this instance it wouldn't "have that covered".

Another reason for installing one could be in properties that are left unheated for long periods of time.

Normally the frost thermostat is set to +5 degrees or thereabouts, but they are sometimes inadvertently set higher than that and start the heating when it wouldn't normally be required.

I'm not a fan of wiring a frost thermostat as per the instructions on the wiring centre lid. IMHO it's a bit of a fudge as it could lead to the property being heated unnecessarily. I think a better way is to wire the frost thermostat in series with a suitably positioned pipe thermostat that turns the heating off again once the pipe system is warm enough to stop the risk of freezing, but not hot enough to heat the property unnecessarily.

Ironically, Honeywell who manufacture the wiring centre also make a kit comprising a frost thermostat and pipe thermostat that enables it to be done properly.

If there isn't a risk of freezing then a frost thermostat isn't required, very few domestic properties have them or require them if the heating is used daily in the winter and if there are pipes in unheated areas they are well insulated.

 

[Ray1000]

Thank you again Stem, now you've explained it - the boiler position was originally inside the un-heated garage which has since been converted into a office, utility room and downstairs toilet. I'll disconnect it later, it will simplify the wiring if nothing else.

 

[ianmcd]

Thank you again Stem, now you've explained it - the boiler position was originally inside the un-heated garage which has since been converted into a office, utility room and downstairs toilet. I'll disconnect it later, it will simplify the wiring if nothing else.

View attachment 268330

That is the pipe stat, you will have to find the frost stat too

 

[Ray1000]

I wrongly assumed it was a frost stat never having seen one ... the system would have been fitted when the house was new in 1998. I don’t think there is anything else.

 

[CBW]

What boiler is it? It may have one built in.

 

[Ray1000]

When the house was built the boiler was an Ideal Classic FF240 which was renewed a few weeks ago for a Ideal Logic Heat 18 the pipe stat was just left where it was.

 

[Ray1000]

Now I know what a Frost Stat looks like ... there isn't one in the house.

It is a detached house and the boiler was in the integral garage now a utility room ... would the frost stat have been in the garage? ... I see in the installation guide for that boiler it says the frost stat needs to be sited in a cold place but where it can sense heat from the system ??

If there ever was one I imagine it was removed and the related pipe stat left in?

 

[ianmcd]

If you follow the cable from the pipe stat you will find the frost stat it will look like a room thermostat that you cant turn