Combi boiler timer - replace mechanical with digital

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My landlord has fitted a new boiler, Ariston E-Combi 30, with an archaic mechanical timer. In the 21st century I at least want a heating advance button, and 7-day timer would be nice too, so I'm trying to fit a digital replacement.

The mechanical timer is a Grasslin FM/1 QRTUZH. Looking at Grasslin's range of similar timers I guessed the FMD 120 would do the job. But it's not working. Before connecting I can set the time and the programs thanks to the internal battery, and that's all I can do afterwards. It won't show me if it thinks the boiler is on, and the boiler does not come on, even when pressing the advance button. Apparently some features on the display only work with power connected so it seems like it's not getting power.

Alarmingly, Grasslin's datasheet from their website shows the FMD120 as taking DC current on pins 1 and 2, same as the diagram on the back of the mechanical timer, giving me confidence I was buying the right thing, but on the digital timer itself it says 230V AC!

The mechanical FM/1


FMD120 datasheet http://www.graesslin.de/cms/products/datasheets/en/fmd120_220_150_250_emd_120.pdf See bottom of last page for pins 1 and 2 marked as "+" and "-", so DC, right? And FMD120 itself


Perhaps my mistake is in not understanding all the "resistive load" stuff on the data sheet, but even an Electronics GCSE and Physics A level didn't teach me what that is!

So to the questions...
Are there lots of sub-types of the FMD 120 (and I have the wrong one for my boiler) or will no FMD120 work? What will work? Or should the FMD 120 work and mine is defective?
 
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I don't think you can assume from the datasheet that + and - mean DC - the datasheet clearly states the thing works of 240V.

The timer may have been modified for use with the boiler but the case / model number not updated. A google suggests the standard model of that mechanical timer also works on 240V AC.

Can you test the supply to the timer from the boiler and confirm it's a 3V DC supply?

To use the replacement timer you have bought you need to find the boiler's permanent 240V AC supply and wire it to the supply pins of the timer. Make sure 240V cannot accidentally connect back to the boiler 3V output. Then use the isolated switching contacts to switch the boiler.
 
Thanks for the reply. I don't have a multimeter to hand so I can't check the voltage (but probably about time I bought one). The power is fed off the PCB for the control/LEDs/etc over very thin wires, I'd be surprised if it's 230V, but I'll check before going further.

If it is 3V like the mechanical timer says, I don't fancy trying to wire some extra connections in (it has to pass a safety inspection!) so I can see the digital timer will heading to ebay. I got it cheap so shouldn't be a loss.

I have now found Ariston's part number for a replacement digital timer, 3318463, but theres no more details on what it is. (It's in their "brochure" which I had foolishly dismissed as being just a pretty picture document.) There are a couple of retailers selling it, equally scant on product details, so I'll make some phone calls next week to find out some more. Although £40-50 for what is basically a digital watch seems more than a bit steep - not to mention what I think of the alleged RRP of £80.
 
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You can wire any controller you like into the Ariston boiler, provided it has volt free contacts. The 240V AC supply for the timer supply, and the control terminals, are on the Ariston PCB - extract from their manual. Removing the link disables the internal timer, which could be reinstated at any time.

Manual at

ARISTON

Page 34:

 

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