How to wire Horstmann C7 programmer to Worcester 24CDi?

[trionic]

My home's central heating is currently controlled by this Honeywell room thermostat:

Which controls this Worcester 24CDi boiler:

The thermostat is going increasingly haywire, and its actions have little to do with room temperature Also, the mechanical programmer on the Worcester boiler has broken.

I wanted a programmer that worked, finer control over the central heating and a non wacky thermostat. So I bought a Horstmann C7 from Screwfix:

I cannot work out how to wire up the Horstmann to the Worcester I'm happy to do the installation, but don't want to cross wires! The Horstmann's installation instructions don't help.

This is the wiring for the Worcester's mechanical programmer:

This is the wiring to the current Honeywell room thermostat:

This is the wiring panel on the back of the Horstmann:

And these are the instructions for the Horstmann, showing what I believe is the correct diagram for my setup:

I know very little about central heating systems, but am good with other types of DIY (car maintenance). I have multimeter, tools... just need to know which wire to put where

 

[breezer]

some times it is easier to remove what you have on the ends and start again, that way you can follow the drawings

 

[ollski]

honeywell to centaur
1 to 1
3 to 2
2 to 4

 

[chrishutt]

Firstly, you will only use the red and yellow wires from the old stat to connect to the Horstmann, using terminals 1 (red) and 2 (yellow). The blue (neutral) wire will have no function on the Horstmann but can be connected to terminal 4 just to keep it out of harms way. It looks as if there is no earth terminal on the new stat so you should just cut the earth wire back so the loose end can't touch anything.

You also need to by-pass the Worcester clock function. The easiest way to do that is to switch the small lever at the side to the "on" position, so the timer settings will not have any effect. you could also set all the tappets to the "on" position so even the "timed" position will not interfere with normal function. It's also possible to change the links on the timer to make it permanently on, but that is unnecessary if you keep the timer switch at "on".

 

[trionic]

Thank you for the replies... I'll get wiring today

Just one thing though: when the Honeywell thermostat switches off, the boiler goes through a cool-down cycle. With the Horstmann wired as described, will the boiler no longer do the cooling cycle? Would that damage the boiler in the long or short term?

 

[ollski]

Thank you for the replies... I'll get wiring today

Just one thing though: when the Honeywell thermostat switches off, the boiler goes through a cool-down cycle. With the Horstmann wired as described, will the boiler no longer do the cooling cycle? Would that damage the boiler in the long or short term?

Don't worry it's controlled by the circuit board on the boiler.

 

[trionic]

Hurrah! Just the answer I was hoping for

Thank you for all your help. If any of you own a Saab and need help with that, then check out the SaabCentral forums. I'm one of the "C900 Workshop" moderators

Now to search the forums for the reason my boiler won't hold pressure!

 

[trionic]

Programmer installed and working great! Just a bit of paintwork to sort and it's done.

I now wake up to a warm house, and come home to a warm house

Thank you again for your help

 

[rjtaylor]

I'm trying to copy this set up so am resurrecting an old thread.....

I need advice on the connection to the boiler which sadly this thread doesn't give. This is the thermostat connection in the boiler (N,LS,LR):

This is presently connected to the mechanical timer:

How do I use these connections to the thermostat?

Do I disconnect the mechanical timer? chrishutt's post seems to state otherwise?

Thanks in advance.