Central Heating Programmer - Electrics

[Bonce]

Hello,

Firstly I apologise if this is in the wrong section but I decided it really was more to do with the electric set up as opposed to plumbing. Secondly I will not be attempting this on my own without professional help but being a bit of a saddo and being interested I do like to understand what is going on! Thirdly sorry for the length of the post now I have reread it, it's a bit long!!

I've just purchased a FP715 Si Danfoss controller as my old one seems to be on the blink (wiring diagram for new controller can be found at this link...hopefully!)

http://www.screwfix.com/search.do;j...tton.x=0&searchbutton.y=0&searchbutton=submit

I don't know what my old controller is but it seems to match the Danfoss i.e. have the same number of terminal connections etc.

My central heating system is a very simple, gravity fed system, 1 zone, no TRV, no room thermostat.

The electrics on my house are fairly old and I have no idea if what is currently in place is right and will confirm with the current regs. It does all work but in having to change the controller I woud like to bring it up to current regs and do it in what would be considered the standard way.

The current set up is as in the following first 2 attached diagrams (bottom of post) So basically it looks like the live feeds from the pump and the boiler is carried in some 3 core and earth cable to an FCU and then onwards to the controller.

So my question is.... if a professional was starting from scratch how would the cables be run etc. There will need to be a JB at the current location (near the pump and bolier) as the flex from the boiler and the pump is short - presumably as this is under my lounge floor this will then need to be a maintenance free JB. Also I have read about the honeywell 10 way heating control box should one of these be used between FCU and controller ? Are these maintenance free? or are they set into a wall and made accessible etc? There isn't much room where I want to relocate the controller.

The Danfoss is described as a 5 wire installation. My attempt at what I think may be right is in the last diagram - and I am not sure but think that the 5 wire installation may mean I am able to get 5 core cable or something? I don't know about any of the colours in this.

I would be very grateful if anyone could let me know as to what professionals would normally do.

Thanks in advance.

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• Bonce
• 11 Jan 2009
• 1

Untitled

• Bonce
• 11 Jan 2009
• 1

Untitled

• Bonce
• 11 Jan 2009
• 1

 

[Taylortwocities]

If you have just a gravity system then you can only control the boiler on/off. Not water and heating separately.
So just concern yourself with the controller connxs. Set the contyroller to gravity mode and follow the new for old table that Danfoss provide.

PS the Screwfix link does not work.

 

[Bonce]

Thanks for that Taylortwocities, don't know why the link didn't work but I have amended above, but need to click through to get to the instruction manual.

And yes I can only control the boiler on off and the pump for the central heating system i.e. can have DHW on its own but not heating on its own the DHW must be on at the same time.

 

[Bonce]

I have been reading other posts with interest about central heating control centres and the use of 5 core flex but am unsure whether it is permissable/ a good idea to use 5 core flex between the control centre and the controller and what the standard colours are i.e. what is usually used for mains live and neutral and then DHW on, CH on and earth and whether these are usually connected to any specific terminals in the control center 1 - 10.

I have read in a couple of posts that solid conductors are necessary for heating circuits, is this true and will this mean I can not use the 5 core flex as I intended?

Again I am not going to do this myself and will get the pro's in but thanks to anyone who has the time to reply it is much appreciated.

 

[Taylortwocities]

Solid conductors are not necessary on ANY circuit.
Not even wiring under the floor, between sockets, for example.
The only criterea is that the cable is sufficient to carry the max current that the fuse protecting the circuit will allow,

Any colour wire can be used for anything but there is a convention that says that live, neutral and earth must be marked as such (brown, blue and green/yellow) and any conductor that may become live should be sleeved brown.

I have to say that I've never seen that in a central heating wiring centre - except for the ones that I've done!

If you use multi core cable, one of the cores must be an earth conductor.

 

[Bonce]

Thanks once again Taylortwocities.

 

[kevin1234]

what does DHW stand for in this controller, and is anyone willing to explain how this works as i am really willing to learn how the heating system works, i have not had experience in heating so willing to learn

thanks

 

[JohnD]

DHW
domestic hot water
in your case, the flow to the hot water cylinder

if your radiators are fed with a pump, you REALLY ought to have a room stat to turn the CH pump on and off dependent on temperature.

IIRC it is possible to fit a Cylinder Stat and a zone valve so that water goes to the cylinder only when required, but I don't think I know where the wiring diagram is for that - gravity feed is very old fashioned now. I think I got Drayton to send me a diagram for it as it is not included in the normal literature. The zone valve has to permit CH to run even when DHW is off, which is not the way your system currently works.

I am just a householder and found the gravity control difficult to grasp

 

[turbodeas]

I'm just a household too, and my 2 bed flat has an ancient gravity system.

It seems very inefficient to not be able to properly divert the boilers hot flow to where it's needed, and to add insult to injury not be able to accurately control the temperature of rads or tank via thermostats!

I'd see about getting a valve and roomstat and cylinder stat fitted and integrated with your control system, I bet you'd save a fair bit on fuel bills if you were able to just heat the water in the summer!

Cheers,

Chris.

 

[Bonce]

Sorry if this is an obvious question but has anyone used one of the Honeywell wiring centres in the above diagrams?

Do they have cable clips and push fit connectors? I am asking with respect to accessability. Shouldn't all junction boxers now be accessible? I was intending to place mine under a floorboard which when carpeted would not be accessible and therefore I believe would not meet regulations.

Basically are the Honeywell boxes classed as maintenace free? Any help much appreciated.

 

[twgas]

I wouldnt put a junction box (or wiring centre, as its known in heating systems) under the floor.
I also wouldnt use a honeywell wiring centre.
the push in ones are called smart fit, I dont think there is one for a 'c plan'

 

[Bonce]

Thanks for reply twgas.

Could you give recomendations of what I should use? or how you would do it? If I was to do as in the above diagrams I would need to make the connections somewhere for the 5 core flex. I just assumed something like a wiring centre/JB would be the norm.

I'm not doing it myself by the way I will get a pro in but I am interested.

Thanks once again your response is very much appreciated.

 

[gas4you]

The new danfoss wiring centers are brilliant. Easy and clear to fit and understand for anyone

 

[D_Hailsham]

My central heating system is a very simple, gravity fed system, 1 zone, no TRV, no room thermostat.

You should definitely get a room thermostat installed and, if affordable, TRVs on all rads except the one nearest the room stat..

The electrics on my house are fairly old and I have no idea if what is currently in place is right and will confirm with the current regs. It does all work but in having to change the controller I would like to bring it up to current regs and do it in what would be considered the standard way.

This is giving an electrician an open cheque to rewire the whole house! There is NO requirement to bring a house up to the current regulations. Remember the old adage: "If it ain't broke don't fix it!"

Ideally you should convert your system to fully pumped, but if this not affordable or would involve too much re-plumbing, you should consider converting your system to a C Plan. This retains the gravity Hot Water and pumped Heating, but gives proper control over Hot Water times and temperature. You can read about it Here (open the two pdfs shown on the left).

Wiring centres aka junction boxes are essentially maintenance free, but you need to be able to get to them in case you have to change any of the components connected to them.

It would be a good idea to replace the FCU with a simple fused spur (3 amp fuse) and wire everything into a 10 terminal wiring centre, as shown in the Honeywell leaflet, - the junction box for pump and boiler may need to be retained.