Digistat +2RF/+3RF with no lights lit (Removing it from my boiler)

[MagMrMax]

I have a Digistat +2RF/+3RF wireless thermostat and SCR (pictured below) connected to a Saunier Duval Semia Condens F24 E boiler.

This morning, the receiver (SCR) malfunctioned out of the blue. No lights are lit on it and cutting the power and restoring it makes no difference.

In similar questions posted here and elsewhere, the suggested solution seems to be, "Buy a new wireless thermostat and SCR receiver combo."

They're about £90 as a set, though, so is it difficult to remove the cable linking the Digistat SCR to the boiler's circuit board, and hence return to the boiler's own internal controls?

If I remove the SCR cable, will the boiler return to internal control automatically, or must a new link be made internally somewhere, perhaps by re-connecting something that was disconnected when the SCR cable was first installed?

Hot water works fine btw. It's just the heating that is affected.

Thank you.

 

[ianmcd]

Turn off the power via the fused spur, remove the cover on the SCR and put the wires in terminals 1&3 into the same terminal, either 1 or 3 doesnt matter and that is the SCR by-passed and the boiler will come on when you operate it using the boiler controls, you will still have the wiring in place if you decide to replace the SCR with something better in the future

 

[MagMrMax]

Cheers, Ian. I will give it a go.

 

[ianmcd]

Cheers, Ian. I will give it a go.

Let me know how you get on , its easy to do, if you want a better set up I wouldnt go with another SCR, they are very unreliable

 

[MagMrMax]

Hi Ian.

Thank you again for replying.

I did as suggested (putting cables 1 and 3 into terminal 1) and the heating came back on, but now it seems to be on almost permanently.

As per the photo, my boiler has a timer (red circle) with controls for Off, Timed, and On. None of these currently work.

The master control switch (green rectangle), has Winter (CH + HW), Off, and Summer (HW only) settings. Turning this to "Off" or "Summer" is the only control I now have.

Is there a way to reassert the boiler's own controls (red circle), so that I can control the CH properly, as it were?

(P.S., I have never liked the Digistat SCR either, but it came with the house. It's not the first time I've had problems with it, but replacing a part did the trick about 2 years ago.)

 

[ianmcd]

That is because the time clock is set to constantly on, you need to move the little slider to the pic of a clock and set the tappets to what times you want to be on and off

 

[MagMrMax]

Hi Ian

That unfortunately doesn't work.

In the pic, the red slider is on the "0" setting for "Heating permanently off", but the heating still comes on.
It also comes on when "Timed" is selected but the little grey notches are set to "Off".

At present, the only control I have is to flick from Summer to Winter.

In addition, the radiator temperature dial is set to maximum (in the pic). If I switch to Winter, the heating kicks in (even with the master switch set to "0").
If I then turn the radiator dial all the way to its minimum, the boiler turns off.
Turning the raditor dial back round to maximum, though, doesn't make the boiler re-fire.
To do that, I have to switch from Winter to Summer and back again, and the heating then returns.

It's very odd how the heating comes on even with the master switch set to "0" or "Timed" (but with the timer set to "Off").

 

[MagMrMax]

Hi again, Ian.

I have had to switch the system off as the pressure when the heating is on is racing up from just under 2 bar (in the green zone) up to 4 bar (at the maximum of the red zone).

Naturally, I didn't used to watch the needle move when I had the heating on in the past, but I don't think it used to climb like that. (I could easily be wrong, but I've never noticed it that high before.)

Cheers

 

[ianmcd]

sounds like who ever wired in the SCR has wired it into the wrong terminals and not the External thermostat terminals, can you post a pic of where the SCR is wired into , not a great idea to constantly use the selector knob , the spindles tend to break

 

[MagMrMax]

Hi Ian.

I heartily agree re: the selector knob. It feels flimsy.

I am very much a layman, but why should the thin cable from the SCR to the boiler be left in place, please?
In my naivety, if I were to remove that cable, the boiler would then have no external inputs whatsoever.
It would then (in my theory) just be reliant on its own internal controls (Winter/Standby/Summer and Off/Timed/On, plus the 2 temperature dials for the CH and HW).
Would that be right?

I will try and get a pic now of the cable nonetheless.

 

[ianmcd]

In my naivety, if I were to remove that cable, the boiler would then have no external inputs whatsoever.

If you completely remove the cable (which is an option,) you will have to replace the factory fitted link that came with the boiler, will need a pic of the wiring at the boiler side to tell you what to link

 

[MagMrMax]

Hi Ian

Pix as below.

I really appreciate all this btw.

1. This is the disaster zone I am faced with underneath the boiler and behind the tumble dryer, none of which, I hasten to add, is my doing (but I will tidy it up after this).
Indicated by red arrows is the thin white cable exiting the SCR and moving towards the boiler.

2. The white cable comes up the back of the boiler and then round to the right hand side where it splits into two thinner black cables.

3. This is the wiring diagram on the inside of the drop-down PCB cover. Terminals 39 and 40 are indicated (as that's where the two black cables are wired in).

4. Here, you can see the black cables making their way round from right to left, ending in block M10.

5. And finally, here are the two cables entering terminals 39 and 40 of block M10.

 

[MagMrMax]

In addition, the 2 relevant pages from the instruction manual are below. Thanks

 

[ianmcd]

remove the wires in terminals 39 & 40 and place a link in them , Just a small piece of wire, but be carefull make sure you isolate the existing wires as it could be a back feed effect because the SCR was wired wrong, if you are removing the SCR remove all wiring from it before making the link at 39 &40

 

[MagMrMax]

Hi Ian

I have got it working, but I did it tinkering before I saw your last message.

Please tell me if you think I have done something wrong, though.

In block M6, white cables 18 and 19 were joined by the coupling below.
I looked at the instruction book pages I posted above, and I reversed the process shown for adding an external thermostat.

1. I removed the coupling.
2. I re-connected cable 18 to junction 4 and cable 19 to junction 5 (shown below by a red ellipse).
3. This didn't solve anything initially, so I then re-connected the black cables (which come from the wider white cable from the SCR) to junctions 39 and 40, and all the internal controls now work!

If this strikes you as safe, I'm happy to leave it as it is.

Thank you so much for your help.