Vaillant ecotec plus to S-plan

28 Jan 2009
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United Kingdom
I have fitted Vaillant Ecotec plus 630 and Megaflow. I managed to get central heating to work normally but hot water cylinder only heats up when heating and hot water are both on at same time at programmer. Both 2-port valves are working. How do I wire it through Danfoss 16 terminal wiring block.
I cannot find any info on the net and two 30 minute phones call to Vaillant have also proved fruitless.
It must be simple.
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Does the 2-port valve for hot water open when hot water (only) is selected at programmer, and cylinder stat turned up?

Check whether the valve itself operates, rather than looking to see whether the boiler fires.
Turn on Hot Water and valve opens normally, boiler does nothing, turn stat down valve closes.
From heating 2-port brown wire is connected to term3 in boiler, so tried making link between CH-2-port-brown and HW-2-port-brown wire, both valves remain open and boiler fires, however both valves will remain open all the time becuase of link.
Remove connection and link and connect Hot Water 2-port to term 3 on boiler and valve, boiler and pump operate even turning off cylinder stat closes valve and shuts down boiler as normal, so vavle is working ok. But now the CH does nothing as the HW did before.
The missing link has to be Brown wires to boiler but they must not be linked.
Am I missing the obvious? Spent hours trying wires in different orders and same result.....
Sounds like you have it wired incorrectly. The brown on the valve should be operated from the programmer then cyl stat. The grey on the valve is permanent live, the orange goes back to terminal 4 on the pcb.

All these will be connected via the wiring center.

There should be a clear wiring diagram in the megaflo handbook.
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Followed wiring diagram supplied with megaflo, certain I have that right, just not sure what goes on with term 3 on boiler?
Term 3 is the live feed for the programmer, if it is a 6 series Vaillant.
Terminal 3 is permanent live from boiler for controls etc, terminal 4 is switched live in, ie when there is 240v on terminal 4 the boiler will fire.

I can't make head or tail of your description of the wiring, and I suggest you spend some time learning how the electrics work, rather than just following a diagram. An S-plan system is relatively simple once you understand the basics.

In essence, the control system should put 240v on the brown wire of the relevant valve, valve will open, and the mechanism will switch the grey and orange leads together. Basically, all the greys should be brought together and connected to terminal 3 at the boiler, and all the oranges brought together and connected to terminal 4.

If you read up and still don't understand how it works, I would suggest that you may be better off calling a professional in.
Sorry, family and friends only as I'm a DIYer. Thanks for asking though :)
DIYer? Didn't see that on Vaillant's web site :rolleyes:
Where can I read up about workings of CH electrics?
On a 6 series you have to power the programmer from 3 or the on/off switch on the boiler doesn't work.

The output from the grey or orange goes into 4.
On a 6 series you have to power the programmer from 3 or the on/off switch on the boiler doesn't work.

The output from the grey or orange goes into 4.

Sorry Simon, still have to disagree with this statement ;)
I learned about a lot of these things in college, I was training to be a plumber with a view to moving into heating, and learned everything and anything I could! Unfortunately my health is against me and I'm unable to work full time but still take an interest incase the situation changes. It also happens that my parents will shortly be having an ecotec installed, and the wiring diagram is fresh in my mind :)

I've become curious though, and had a look round on the net, only to discover that it's actually quite difficult to find a page that describes the operation of the system.

These turned up though, and hopefully they may help -

and this should help with understanding how the valve works -

use the above honeywell guide for the wiring.

the only alteration is that the live supply for the connection unit should come from terminal 3 of the boiler pcb. This so that there is only one source of electrical supply to the controls. You don't need all the 16 terminals just 12.
Thanks for all your input. I got it working, to summarize

Term 3 on boiler pcb supplies live to programmer, why vaillant don't tell me that in manual......
So, don't wire live on programmer in regular live with greys and browns etc. at wiring centre, instead run from term 3 on boiler to live on programmer. Obvious!

Couldn't have done it without you ;)

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