s plan wiring confused

eeb1933 · Dec 11, 2010

hi all

i'm having a nightmare day. having a new heating system in s plan using glow worm fexicom 18sx boiler. not done a s plan for a few years as combis are taking over so followed the wiring diagram as by honeywell etc show. went live today all works but when the room stat turns off or hot water turns off boiler turns off. plumber said this must have a permanent feed all the time because of lcd screen etc. i just can't get my head round how to get round it! the boiler has L N E and room stat connections for v free room stat which has the link in. if the boiler has permenant feed it fires up and all controls won,t shut it off.

can anyone show me where i'm going wrong. many thanks

NozSpark · Dec 11, 2010

On S plans the boiler has a permanent live all the lime..

There are usually 6 terminals

Permanent live

Permanent neutral

Earth

Switched live

Pump Live

Pump Neutral

The boiler usually provides pump over run, that's why you wire the pump from the boiler.

sellers · Dec 11, 2010

not on all noz. Older boilers use the standard s plan diagram where the boiler uses a switched live when called for, like the s plan diagram shows.

But you are right that most new boilers need a perm live. So what I generally do is wire to the boiler in 5 core flex, Giving LNE, then the switched live, which goes into connection 10 on the diagram. This lets the boiler know when to fire. If your pumps in the boiler then this is all you'll need.

If your pumps outside of the boiler and your boiler needs a pump over-run to work. take your pump live out of connection 10, and connect it to the spare core you have left over in your 5 core. Then connect the other end at the boiler to the Pump Live. Have a look in your boilers instructions to see if you need a pump over run.

hope this helps eeb

sparkytim · Dec 11, 2010

If your boiler has PERMANENT live ONLY and no Switched live terminal then the S Plan Spring return valve switching contacts (ORANGE and GREYs) will need to be VOLT FREE and connect to your VOLT FREE ROOM STAT terminals in place of the link.