S plan plus (zoned) with combi? Help required

19KD75 · Jul 9, 2011

Hi guys, I have offered to help a neighbour out by wiring up their new CH.

They have the following kit:
Honeywell ST9500C controller
DT90e thermostats (one upstairs, one downstairs)
2off 2 port valves
Worcester Bosch 25si condensing Combi

They've lost the wiring diagram for the controller - I've looked on the web, but can only find diagrams for S plan plus with system boilers, not combi

Can anyone on here help me out?

Dunc · Jul 9, 2011

Just google the boiler make and model with the words 'installation manual' after it. All Worcester Bosch boilers have the instructions online in PDF format. As for the programmer the connections will be labelled on the back of it underneath the connection plate. Just wire it up as a normal S Plan then, only difference being the HW zone is now a CH zone.

grimysparks80 · Jul 9, 2011

The oranges on the valves will go together in the boiler switch live. greys are permanent live. brown on each valve will be connected to the switch feed in from the appropriate room stat.

nickblake · Jul 9, 2011

I may be wrong on this but im sure its the Ls and Lr terminals on the left hand side of the circuit board you need may have a link you need to remove , so if you wire it ,out put of the programmer heating , these will go to the inputs of the room stats then the out puts of the room stats to the browns of the MV's obviousley the blues of the Room stat and MV go to neutral if you connect the grays to the Ls terminal and the orange to the Lr terminal with the LNE to the boiler for its supply when you have a heating demand fromm the room stat this will operate the MV once this has opened will operate the micro switch (gray and orange ) thus firing the boiler

i may be wrong but im sure its the Ls and LR its on the circuit 3/4 the way from the front to back left hand side

Kev the gas · Jul 10, 2011

Welcome all, first post to this forum.

L N E as usual to the boiler.

Ls is live to the control system ie timer, stats and zone valves.

Lr is switch live to the boiler

Ns is neutral for controls.

The boiler is in charge !!

Kev.