Five Questions About a Nest CH & HW Install

[olic87]

Hi All,

New to the forum and see that there has been a lot of help with this subject. I have a Honeywell Smartfit system that is on the blink and needs replacing. The issue is that unfortunately, the valves and cylinder sensors are proprietary; so I need to replace them to fit a Nest or anything else.

I have an HRM Wallstar Oil Boiler (On Ground Floor), Hot Water Cylinder and CH Pump configured in an S-Plan arrangement at the moment (In First Floor Airing Cupboard). I plan on replacing the 2no valves with new 2-port valves with traditional 5 wire cabling and the cylinder thermostat with a new one with a Common, 1 (Call for Heat) and 2 (Satisfied) terminal.

I have attached some images of the Valve/CH Pump arrangement and the existing wiring within the Honeywell Smartfit Base Unit:

I am fairly happy with everything in the Nest Manual. I have attached a sketch of the schematic how I believe it should be installed to:

But have a couple of queries I wonder if anybody can help with:

• I assume that the CH pump Earth and neutral are fitted into the general earth & neutral connector.
• I am not sure whether the pump should be installed in the mains live or the Boiler/CH or HW Valve Lives. I assume that it should only be triggered when a signal to the actuators is given or is it always on and activates when water is drawn across it?
• (Helpfully!) My boiler has a Switched Live (Manual says "From The Timeclock" in brackets) and a Permanent Live (Manual says "Must Bypass The Timeclock" in brackets). I am not sure how these connect. My assumption would be that the Switched Live is wired into the Orange cables from the CH & HW Valves (Into Connection Terminal #10) and the Permanent Live is connected to the mains live (Into Connection Terminal #1).
• The Cylinder Thermostat has a Common and 1 (Call For Heat) as the Nest Schematic; but also another terminal labelled 2 (Satisfied). I assume that this is another feedback which other heating systems may need and I can leave it unconnected as the S-Plan Nest arrangement doesn't need it.
• Finally, I assume that if I turn off the boiler and bung the cold cistern in the attic, I can open the valves manually and drain the First Floor heating system only to drain the water around the two valves as it will take all the water out of the radiators and the coil in the hot water tank?

Any help would be greatly appreciated! Thankyou in advance.

Regards,

Oliver

 

[stem]

I assume that the CH pump Earth and neutral are fitted into the general earth & neutral connector.

Yes

I am not sure whether the pump should be installed in the mains live or the Boiler/CH or HW Valve Lives. I assume that it should only be triggered when a signal to the actuators is given or is it always on and activates when water is drawn across it?

The pump should not be permanently powered. It needs to be operated by the controls, but the method used depends upon the boiler. Some pumps are wired directly to the boilers L N & E terminals and go on and off with it controlled by the motorised valves orange wire (terminal #10). Other boilers require a 'pump overrun' to keep the pump running for a while after the boiler goes off to dissipate residual heat. If this is the case your boiler will have terminals provided specifically for connecting the pump to. Your boiler manual will provide this information in the wiring section.

(Helpfully!) My boiler has a Switched Live (Manual says "From The Timeclock" in brackets) and a Permanent Live (Manual says "Must Bypass The Timeclock" in brackets). I am not sure how these connect. My assumption would be that the Switched Live is wired into the Orange cables from the CH & HW Valves (Into Connection Terminal #10) and the Permanent Live is connected to the mains live (Into Connection Terminal #1).

Yes

The Cylinder Thermostat has a Common and 1 (Call For Heat) as the Nest Schematic; but also another terminal labelled 2 (Satisfied). I assume that this is another feedback which other heating systems may need and I can leave it unconnected as the S-Plan Nest arrangement doesn't need it.

Correct, the Satisfied signal is used when a 3- Port motorised valve is installed, instead of two 2-Port valves. As you have figured, the S-Plan doesn't need it.

Finally, I assume that if I turn off the boiler and bung the cold cistern in the attic, I can open the valves manually and drain the First Floor heating system only to drain the water around the two valves as it will take all the water out of the radiators and the coil in the hot water tank?

In theory. Depends how good your "bung" is. If there isn't an isolation valve in the supply to the feed tank, and you don't want to fit one, the usual way to isolate it, is to put a piece of wood across the top of the tank, and tie the ball valve float up to it.

 

[olic87]

Stem,

Thanks for the reply, I think I have figured it, the manual for the boiler is online here HRM Wallstar Boiler (Page 27).

As such, I think the way the boiler calls for power means I wire it up as follows:

And thanks for your tip with the header tank, I have a bung; but think I will go belt and braces and prop the ball valve anyway. Also found a duff gate valve that I think if I replace will make life much easier if I need to mess about with this in the future.

Just need to wait for the weather and my spare time to align... every day I have planned to do the work it has either snowed or been too cold to turn the heating off for the day!!

Thanks for the advice, if you can look at the schematic/manual (page 27) and let me know if you think I am on the right track that would be great!

Cheers,

Oli

 

[stem]

As you make reference to page 27 of the manual, this relates to the 'System Wallstar' version of the boiler. (not the standard version*). In which case the wiring to the boiler is correct as per your sketch:

However also on page 27, it also says that the 'System Wallstar' also has a pump connection lead supplied with it. This should be used to connect the pump.

*The standard version of the boiler [Page 20] is different. It doesn't have the pump connection included.

 

[olic87]

Ah sorry my bad, it is the standard one not the system, no pump wiring to the boiler sounds like standard boiler on of 20 works as my schematic too.

Thanks for your advice,

Oliver

 

[olic87]

Just to say that I got round to doing the swap over today, and although it took all day - touch wood it all seems to be working! Glad to say that stem's advice was sound and a great help!

Thanks,

Oliver