CH programmer wiring question

[jon92]

I would like some help understanding the wiring inside my (old) Danfoss programmer, image attached. According to the manual, terminal 3 is HW on and 4 is CH on. The cylinder thermostat is connected across 3 and 5, and the room thermostat across 4 and 6. I assume that 5 also goes to the HW valve (it's 2x2 port layout) and 6 also goes to the CH valve. So I'm wondering a) what the second wire connected to 4 might do, and b) why when tested with power off, the room thermostat calling for heat makes a circuit between 4 and 6 (which I understand) AND between 4 and 5, which I don't. To me that implies that the room thermostat would switch the HW valve as well as the CH valve but I must be wrong since the system switches HW and CH separately as expected.
I am looking to replace the room thermostat, hence trying to understand current connections before I proceed.

 

[stem]

Danfoss make a lot of programmers what model is yours?

 

[jon92]

Thanks for a very quick reply, it's a CP15 - fitted in 1995! I scanned the instruction manual and hopefully attached it.

 

[ianmcd]

what is your existing room thermostat and what do you want to replace it with ? if everything is working OK with the existing set up leave it alone and ask for advice on what you are trying to change

 

[stem]

I'm not too familiar with all of the Danfoss variants especially the older versions, but some used all of the 6 terminals. In this case and terminal 1 and 4 would be the HW on and CH on respectively.

However if yours has 3 as HW on and 4 as CH on it would appear that yours doesn't fit into that category, so terminals 5 and 6 probably don't do anything and were merely used as convenient free terminals and were used by the installer for the thermostats

You haven't posted the page of your manual with the wiring details on, what does the wiring instructions say that they are for?

If you want to replace the thermostat with another thermostat (ie not a combined thermostat / programmer such as Nest or Hive etc.,) post details of the old and new thermostat and we can advise. You won't need to change any wiring at the programmer.

 

[jon92]

The PDF I uploaded of the manual seems to have lost part of the page, so I'm trying again with this post.

 

[jon92]

ianmcd - I'm replacing a 20 year old mechanical room thermostat with a Heatmiser NeoStat. I had assumed the A2 output of the NeoStat could be connected to my existing terminal 6 which feeds the CH 2 port valve.

 

[stem]

There you go then, it states "not used" so they are just spare terminals that the installer has used for the thermostat wiring. With regard to the extra wire in terminal 4 that is unusual, I have seen it on occasion where an existing system was upgraded to 'S Plan' and because of the pipe layout the heating needed two motorised valves just for controlling the heating. Is it possible there is another one somewhere? Otherwise, the only way to know where the wires go is to trace them.

 

[stem]

As your new thermostat is programmable, then you will need to modify the wiring at the existing programmer. The existing thermostat presently receives a switched live from the programmer, but the new programmable thermostat requires a permanent live supply instead.

Unfortunately this relates to the wiring from terminal 4, so you will have to find out what both of the existing wires do before we can advise further. I suspect that the red wire in terminal 4 will be the live supply to the thermostat, but you need to confirm that, along with tracing where the yellow wire with the red sleeve goes.