[OpenTRV-dev] OpenTRV install problem

[Adrian Godwin]

Are you using pins 3,4,5 to connect to the boiler ?
It does seem to have a normal mains supply as it's possible to use the
thermostat hysteresis heater. You could try putting a small load in the
same position (ie pins 4,5) - perhaps a 5W light bulb or anything that
meets the minimum load for the SSR.

I have the same boiler, but it's connected to a Vaillant controller (I
think via eBus).



On Mon, Jan 27, 2014 at 7:34 PM, Damon Hart-Davis <EMAIL ADDRESS HIDDEN> wrote:

> Hi,
>
> An odd one: I wonder if any of you can offer any optinions or solutions
> (and it’s something that OpenTRV is likely to deal with in other boiler
> installs).
>
> On an installation today, now with 5 OpenTRV-controlled rads and a
> separate unit only doing boiler control:
>
> Boiler: Valliant ecoTEC plus 837
>
> http://www.vaillant.co.uk/mediaarchive/2013/09/ecoTEC-plus-installation-service-manual.pdf
> Controler boiler end: Drayton Digistat SCR (part of Digistat RF system)
>    http://www.draytoncontrols.co.uk/WorkArea/DownloadAsset.aspx?id=28360
>
> There is a problem in that though the SSR indicator LED operates
> appropriately, eg in response to call for heat (so the hub is working), the
> boiler never seems to go off as if the zero-switching SSR (crydom
> D2W203F-11) does not ‘release’.
>
> There are some off voltages seen across the ‘call for heat’ contacts (with
> the SSR and normal controller removed, boiler on):
>
> DMM VDC: 0V
> DMM VAC: ~200V (cf mains ~235V)
> 30kOhm/V analogue MM: ~220V
>
> So it seems to be AC and near but not quite mains.  (Not the 24V
> alternative that can be used with the boiler.)
>
> I wonder if thie boiler is being ‘clever’ and either the circuit is high
> impedance (too high for the SSR to power itself correctly) or some such.
>
> Any ideas?
>
> If for some reason I cannot use a normal ZC SSR there, I may have to use a
> real old-fashioned relay (I can’t find an SSR that provides the volt-free
> 24VDC—240AV volt-free switching that the Drayton SCR unit manages), driven
> somehow from the logic 3.3V output from the OpenTRV unit.  Is there a neat
> unit that I can use to do that, small and low power and that I can stick on
> the wall in place of the SSR box?
>
> Rgds
>
> Damon
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