I have a "Sime Super Four" combi-boiler system installed in the loft. This has a built-in programmable clock which I would like to replace with something like a DanfossFP715.
This will provide me with the useful manual and +1hr overrides, but the main reason is to have the controls (programmer) in a more convienent place and not having to pop into the loft access the controls.
The Sime has a circuit diagram which shows the switches for the CH and DHW and it looks fine. However, when I look at the wiring for the Danfos, it is showing a live feed switching to either on/off for the 2 switches (SPDT) sending 230V to either.
The Sime looks like it is actually making/breaking a circuit, and the small PCB has at least some 24volt components.
Anyone familiar with this boiler and know if I can easily replace the programmer ?
I have BMP images of the Sime circuit, and a PDF file for the FP715, if anyone is interested enough to have a look.
In order to fit external timers to most combi boilers, you need timers with volt-free contacts - where the contacts are completely isolated from whatever drives the timer itself. You could safely use (say) a Honeywell CM67 which is battery driven and definitely has volt-free contacts. It doesn't do your +1hr in quite the same way as the Danfoss, but it can achieve the same thing - and more - with its 'party' setting, and has lots of other clever tricks up its sleeve.
I don't have a spec for the Danfoss FP715, but I suspect that its clock is mains driven (with battery backup) and that the mains is switched through to the CH and HW controls. If so, it will not be suitable for your purposes - unless you use it in conjection with a relay.
Many thanks Set Square. I guess it's "volt-free" switching I'm after.
Am I correct in thinking that I'd need 2 CM67 units - to switch the CH & DHW ? Although I called the Sime Super Fours a "combi-boiler" it has a inbuilt hot water tank (40lt ?) and I' like to 'manage' both from a new remote programmer/timer.
What is the "party" setting ? I'm not too bothered about the +1hour but want some "advance" button where I can override the current situation to on or off until it's next programmed on/off.
I read that the CM67 has radio-frequeny remote temp sensors, which would be nice but not really suitable for me installation. I assume that i can ignore the therostatic features of the CM67 and just use it's timmed switching ?
However, since I'm likely to need 2 units - just what type of main relays switches could I use to provide a similar volt-free switching using the Danfoss ?
I've since found more details of the FP715 - and it definitely switches mains to its outputs - which is *not* what you want.
The CM67 which I suggested earlier is, of course, a programmable thermostat rather then just a timer - so that it replaces a room thermostat *and* a timer. It controls only one channel - i.e. the central heating. However - I presume that, with a combi, the HW is on 24x7 to give hot water on demand whenever a hot tap is turned on - so you don't need a timer for this.
There is also a wireless version of the CM67 so that, if you wished, you could have the receiver in the attic near to the boiler and would not need any wires between that and the room unit.
My previous post seems to have crossed with this one - please have a look at that. But yes - volt-free is what you're after.
I don't think that the CM67 is suitable for hot water. Do you really need to control that - rather than keeping the 40 litre tank hot all the time? Is it lagged?
First a bit of explanation. The CM67, being a programmable stat, doesn't have ON and OFF per se. It simply allows you to specify different temperatures at different times - ranging from 5 degC to 30 degC. So, to turn your heating off, you simply have to tell it to operate at a lower temperature than the room will be at with no heating. For example, mine is set at 10 degC overnight. Now to answer your question!
You can at any time temporarily over-ride the programmed temperature. The over-ride will continue until the next programmed event. The 'party' setting allows you set a different temperature from the normal setting for a given number of hours, regardless of programmed events. For example, if your heating normally goes to the overnight setting at 11pm - but you are having a party, and want the house to be warm until 2am, you can set it at the higher temperature for 3 hours. [You can also use it to set a *lower* temperature for several hours if, for example, you are going out and don't need the house to be warm until just before you return].
As per my other post, you *could* use the RF model. And, as above, you have to specify a temperature - but you could use 5 for off and 30 for on if you just wanted it to turn on and off regardless - but that would be a waste. Do you have a room stat at present?
You should be able to get something suitable from Maplin or RS-Components. Essentially they need to have a mains-operated coil switching some independent contacts. You use your FP715 to drive the coils, and use the contacts to control the boiler. Your boiler spec should tell you what voltage/current capacity any external switching device needs to have. You will have to mount the relays in an insulated container - and will probably have to solder up the connections.
Have you got any info on how to implement that facility? I've got a number of CM67RF's and a CM61 and If you move the setpoint either up or down this override is only effective until the next programmed time / temperature change. There is no mention of any "party mode" in either the installation guide or the user instructions.
Why not just use a 'volt free' switching stat/programmer?
The Drayton Digistat range of programmable room thermostats does this, I used one with my combi in the last house for heating control.. This has an override facility until the next programmed change.
If you really feel the need for timer control of the HW as well then you can get time switches as well with volt free switching (you wouldn't want a stat for controlling the HW
The text below (in quotes) is from the instruction leaflet which came with my CM67. There are a load of buttons which you get at by lifting the hinged lid. Immediately under the display is a row of 6 buttons numbered 1-6 for the 6 programme steps for a day. Under these are 3 more buttons - depicting a cup of tea, a rocking chair (I think!) and a suitcase. These are for Party, Day Off, and Holiday settings respectively. This is what it says . .
"When the slider is in AUTO, the temperature can be adjusted temporarily by pressing the (PARTY) button. Set the party time (1 - 23 hours) by pressing [Clock] + or -. Set the party temperature (5°C - 30°C) by pressing TEMPerature ^ or V (up or down). The CM67 will control to the new temperature for the set number of hours and then go back to the normal temperature program. To cancel the PARTY setting, press (PARTY) a second time. The button can also be used when you go out and want to reduce the temperature for a few hours to save energy."
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