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 Post subject: Randall SET2 Replacement
PostPosted: Fri Oct 27, 2017 10:13 pm 
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Hi,

I have an elderly relation with a Randall SET2 programmer Image

which now has developed a fault with the LCD.

I was looking to get a replacement unit for this person. I understand that there are Danfoss (FP975) direct replacements for this that require no specialist knowledge to replace and can use the existing backplate from the original unit.
Is this correct and is it the best solution? I know little about these controllers.

However, is there a better unit to replace the old SET2 with? The FP975 looks like a suitable item. I was just wondering that with minimal effort would there be anything better to replace it with and if so, would they require an electrician to install? I don't want anything too fancy as it for an elderly person.


Thanks.


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PostPosted: Sat Oct 28, 2017 9:13 am 
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As long as the old one definitely has the standard back plate then most new programmers are available to you.

Personally I fit the Honeywell 9400 ones as I find them easier to understand for the customer, but there is nothing wrong with Danfoss.

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PostPosted: Sat Oct 28, 2017 9:10 pm 
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Hi thanks for the reply.

I was only looking at the Danfoss unit as it has direct heritage with the Randall brand.

As the current programmer can only provide Hot Water or Hot Water and Central Heating - is there any additional work that is required for these new programmers which can provide heat only? I presume as the ST9400C (I have assumed this is the model you use) is only a 2 channel programmer that I do not have to worry about the Heat Only option?


Thanks for the reply, much appreciated.


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PostPosted: Sun Oct 29, 2017 8:36 am 
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The Danfoss programmers have dip switches on the back that are set to the system you have, so probably best to stick to them.

I missed the fact about you can only have HW or heating and HW.

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PostPosted: Sun Oct 29, 2017 9:44 am 
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Just to state the obvious. After powering down and removing the programmer, mark up the cables and take more photos just in case you do need to swap the back plate.

As gas4you said, new programmers usually have a dip switches or jumpers to allow the setting of HW only or HW and CH.


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PostPosted: Mon Oct 30, 2017 8:42 am 
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Okay - I've attached an image of the backplate. Hopefully, someone can confirm that this is the std backplate and I only need to replace the programmer.

As per the previous replies I was looking at replacing it with:
https://www.ebay.co.uk/itm/HONEYWELL-ST9400C-7-DAY-2-CHANNEL-PROGRAMMER-NEW-/263286387876?_trksid=p2349526.m2548.l4275

Is this a direct replacement or is there a better option?


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PostPosted: Mon Oct 30, 2017 9:41 am 
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Hi,

I missed the final reply from gas4you which stated that I'd be best sticking with the Danfoss range.

Is there any one specifically between the Danfoss FP975 and the FP715 that I should opt for?
I was reading up here, but could not seem to fathom the real difference between the two devices:

http://www.electriciansblog.co.uk/2016/11/how-to-find-best-replacement-central-heating-programmer-timer-control-honeywell-horstman-drayton-potterton-siemens-danfoss-randall/

Both have 3 on/off per day - although the FP715 is defined as 2 on/off / 3 on/off (selected at installation).


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PostPosted: Mon Oct 30, 2017 6:57 pm 
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I have only ever fitted the 715, so cannot comment on the other, but the 715 is ok

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PostPosted: Mon Oct 30, 2017 10:39 pm 
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Father Ted wrote:
As the current programmer can only provide Hot Water or Hot Water and Central Heating - is there any additional work that is required for these new programmers which can provide heat only? I presume as the ST9400C (I have assumed this is the model you use) is only a 2 channel programmer that I do not have to worry about the Heat Only option?

The old C plan was like this.
Image
There is no motorised valve and not cistern thermostat most programmers had both physical and dip switched to give 10 programs, so the hot water was thermo syphon there was no way hot water could be turned off, altering the programmer may allow you to select it, but you will always have hot water it can't be turned off.
Image
There was a slight improvement where you could switch off the boiler in summer months when hot water reached temperature but still in the winter hot water would get rather hot.
Image
The final C plan has a motorised valve and with these you can change programmer to 16 rather than 10 option mode.

I have seen even with a S plan where some one has fitted the programmer and got the internal switches wrong, but in real terms if you have motorised valves then 16 programs, and if no motorised valves then just 10 programs.



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PostPosted: Tue Oct 31, 2017 10:37 am 
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Thanks for that info. I'm hoping just for a straight swap of the programmer at this stage as the system is getting old and I don't want to be making any more changes than the minimum.

So, in terms of the programmer, is the FP715Si the one to go for? I've checked the wiring diagram and it is hard to tell definitely without tracing things back fully, although I can see the links L-2 and 1-5 in the above image are as per the plan, that is all I can confirm.

At this stage, just looking for confirmation that the FP715 will be a direct replacement and is the most suitable device. I think that is what you are telling me. Just looking for confirmation prior to purchasing the device.

Thanks.


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PostPosted: Wed Nov 01, 2017 1:54 pm 
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Hi,

So others can see the conclusion of this story, only the Danfoss FP975 is a direct replacement for the SET2. The FP715 has a different wiring plan.



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PostPosted: Mon Nov 06, 2017 7:05 pm 
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Fitted and now working. However, the backplate supplied with the FP795 had to be fitted as well due to the connection for the blades being too shallow for the FP975.



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PostPosted: Mon Nov 06, 2017 7:24 pm 
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Glad all sorted thanks for update

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