S Plan wiring using a Low Loss Header and a single System Boiler running 2 pumps

[Elforleather]

In case anyone has an interest I completed and commissioned this system on Friday as planned and it is running beautifully, the pumps are doing a text book job and the DHW and Heating circuits are performing perfectly.

The relays I used were 15amp SPTT using the normally closed to control the orange switched lives from the zone valves to 10, with the relay coils being driven from the lives from the two stats and there is no pump conflict. The Magna1 was expensive but the trade off for the customer was worth every penny and he says he's never had heating like it.

I used a Worcester Bosch LLH as I liked the insulation pack it comes with and everything is very very quiet.

 

[chris watkins]

Good stuff Elforleather, its nice to know that everything is working sweat as a nut after all the tips & advice you followed after posting on here!! LOL :wink_smile:

 

[newcastle phill]

Enjoyed this post :thumbup:

 

[Elforleather]

The saga continues....... Gents, I have something of solution for this but thought it may be something you were interested in or maybe you have something better?

The system runs, but I needed to fit the outside temperature compensator in. The problem is that its switched live should, according to the MI, connect to the HW off connection usually at 7 in the wiring centre. Trouble is that the honeywell 9420 has a five wire format and there is no HW off, 7 is vacant. If I use the switched live at 10 then the OTC will, inadvertently, effect the boiler when it's trying to satisfy DHW.

So, I can rig a normally open relay onto the HW zone valve brown and create a hot water off live feed, but does anyone know a better way of wiring an OTC to and S Plan with a five wire programmer?

 

[Nostrum]

Not quite sure I get you but could you take it from cylinder stat satisfied?

presuming you want it to be off (no sw/l) when h/w has demand?

 

[chris watkins]

So you don't want an S plan after all but a system wired with priority hot water by the sounds of it?
Shame you didn't mention this when you first posted !!

Am I right in thinking you need to signals (SWL's) to the boiler one for HWS & the other for the WC heating ?

 

[Nostrum]

I read it as the weather compensation has its own sw/l which would come from h/w off on programmer?

 

[doitmyself]

the honeywell 9420 has a five wire format and there is no HW off,

The 9420 installation manual shows 6 terminals:
N
L
1= HW OFF
2= CH OFF
3= HW ON
4= CH ON

 

[Elforleather]

To be honest I assumed that 1 and 2 were actually not valid.live as honeywell don't refer to them in issue 16 of their book. You have a good, and valid point, I'll get my meter across them and check it out.

The bottom line, as you suspected, is that I need to tell the OTC that the HW is not in demand so that it won't impact on the heating. The OTC kit from Ideal has it's own relay to isolate the device when HW is being produced, so if 2 on the programmer is a live feed then problem solved.

 

[Elforleather]

Hi Nostrum, yes you read it correctly, I just need the SL for the OTC to know that the HW is not in demand.

 

[doitmyself]

To be honest I assumed that 1 and 2 were actually not valid.live as honeywell don't refer to them in issue 16 of their book.

I assume you are referring to the diagram on page 5 of the Wiring Guide. The reason it does not show terminals 1 & 2 (HW OFF and CH OFF) is that they are not used in S Plans. The Y Plan diagram on page 9 does show terminal 1 as it is used.

The bottom line, as you suspected, is that I need to tell the OTC that the HW is not in demand so that it won't impact on the heating. The OTC kit from Ideal has it's own relay to isolate the device when HW is being produced, so if 2 on the programmer is a live feed then problem solved.

Do you mean Terminal 1, which is HW OFF? Terminal 2 is CH OFF.

I take it that you are not using the Ideal Kit. Why not?

It might be a good idea to read the Installation Manual to see how it works. It's not so simple as you appear to think.

 

[Elforleather]

Yes I did mean terminal one, sorry, mine was a typo.

I am using the Ideal unit, the one delivered to me was missing a relay and instructions, I called Ideal and they were unsure if the kit was designed for a a heat only or combi boiler and put in the wrong box, I think the box had been robbed at some point, I should have a new one tomorrow.

I'm sure all will become evident.

 

[doitmyself]

I am using the Ideal unit, the one delivered to me was missing a relay and instructions,

The combi kit and heat only/system kit are different part nos! The combi version does not include a relay as it is not needed.

Combi = 204914
Heat/System = 206152

 

[Elforleather]

It turned up today and all fitted and working now. I had the right part first time, but someone had liberated the relay from the box. I've fitted them I the combis before so knew the difference.

I had a free wire for the control centre so picked up the HW off at the programmer as you said, many thanks for that, I should have twigged myself.

My only struggle now is getting the customers to understand how it functions. I always find that's the toughest challenge. I did the Worcester FX controls course on Wednesday and sadly their latest range including compensator is as clunky as ever Worcester controls are with nothing very new or useful.

 

[doitmyself]

My only struggle now is getting the customers to understand how it functions. I always find that's the toughest challenge.

Particularly making them understand that the rads do not have to be boiling hot all the time.