C-plan with programmable thermostat?

[smudgersmith1]

Is this possible? I have a honeywell st9400c programmer and controller which is wired to dial-type thermostat and hot water actuator valve.

Being a novice, I bought a Danfoss tp9000 programmable thermostat with hot water function, thinking it would be an easy swap but now I've come to realise it may not be possible.

I would like to be able to have the heating set to different temperatures during the day. Can it be done with a c-plan system??

 

[stem]

The C-Plan provides independent control of the heating and hot water, so all of the functions provided by the Danfoss TP9000 will work with C-Plan.

All of the C-Plan components must be present though, as shown below (Room Thermostat / Cylinder Thermostat / Hot Water Zone Valve) Although they don't all have to actually be Honeywell. Other makes are available.

Assuming all the parts are present, and they are wired correctly now, then it shouldn't be too difficult to swap them over. The two programmers even use the same terminal numbers for the same functions. Terminals 1 & 2 won't be used with a C-Plan.

Honeywell ST9400C

Danfoss TP9000

 

[smudgersmith1]

Thanks very much for your reply. All of those items are present.

At the minute, the thermostat is wired into the controller (honeywell sundial I believe). I take it that I need to remove the existing thermostat wiring and wire the new danfoss thermostat into the danfoss programmer...

Photo of existing wiring to programmer attached.

 

[Wildcat1961]

All of the C-Plan components must be present though, as shown below (Room Thermostat / Cylinder Thermostat / Hot Water Zone Valve) Although they don't all have to actually be Honeywell. Other makes are available.

Note that not all 28mm two port zone valves utilise the auxiliary switch (6 wire) which is required for the sundial C plan, Tower being one manufacturer that supply the 28mm two port with a 5 core flex (no auxiliary switch).

 

[Wildcat1961]

Thanks very much for your reply. All of those items are present.

At the minute, the thermostat is wired into the controller (honeywell sundial I believe). I take it that I need to remove the existing thermostat wiring and wire the new danfoss thermostat into the danfoss programmer...

Photo of existing wiring to programmer attached.

The C plan doesn’t require a switched live from the programmer ‘HW off’ terminal, are you sure this is a C plan arrangement?
Possibly the HW ‘off’ from programmer has been parked-up in wiring centre to make safe and not being used?

 

[stem]

Terminals 1 & 2 won't be used with a C-Plan.

The C plan doesn’t require a switched live from the programmer ‘HW off’ terminal

But in the photo you do have a wire connected to terminal 1. The 'C-Plan' only uses the Hot water on (3) and Heating on (4). The microswitch in the motorised valve has a changeover contact that provides boiler control.


C-PLAN

It's the 'Y-Plans' systems that have a three port motorised valve use Terminal (1) 'Hot water off'.

 

[Wildcat1961]

But in the photo you do have a wire connected to terminal 1. The 'C-Plan' only uses the Hot water on (3) and Heating on (4). The microswitch in the motorised valve has a changeover contact that provides boiler control.


C-PLAN

View attachment 136784


It's the 'Y-Plans' systems that have a three port motorised valve use Terminal (1) 'Hot water off'.

Yes I’m fully aware of the sundial wiring configurations.
It doesn’t matter what the photo shows it’s not required.
C plan wiring configuration shows HW off from programmer parked-up on its own within wiring centre.

 

[Wildcat1961]

 

[stem]

Wildcat1961. I think you may have misunderstood my last post, I wasn't contradicting you, I was agreeing with you. A C Plan shouldn't have a wire in 1.

 

[Wildcat1961]

Nor should an S plan unless using MOMS valves.

 

[smudgersmith1]

I'm not certain that it's c-plan so any informed advice is welcome. But isn't the wire in 1 an earth??

 

[Wildcat1961]

isn't the wire in 1 an earth??

The ‘earth’ as you call it will carry mains voltage whenever HW is set to off at programmer.
Blame the lazy installer for using 4 core + earth.

 

[stem]

I'm not certain that it's c-plan so any informed advice is welcome.

Do you have a 3 port motorised valve? Something like the one below? If so, you have a 'Y-Plan' which would still be OK for a Danfoss TP9000. The wire in 1 would be moved across from the Honeywell ST9400C with the other wires.

Untitled

• stem
• 1 Apr 2010
• 8

Just out of interest, what was it that made you come to the conclusion that you had a 'C Plan' system?

 

[smudgersmith1]

Yes I have one of those! Sorry for the confusion!

What do I need to do with the thermostat? Do I just replace existing with the danfoss sensor? Doesn't the danfoss sensor need to be wired into 5 & 6 in order for it to read the temperature?

 

[stem]

Yes, terminals 1, 3, 4 swap over as they are, and terminals 5 and 6 do go to the new sensor. Then either leave the existing room thermostat set to 'maximum', or disconnect it and join the live switching wires presently connected to it together. Safely isolate any neutral (if one is present) you can't just remove the thermostat otherwise you would create a open circuit, and the heating wouldn't come on.