Drayton Digistat +2 works, but not switching heating...

[hsabbers]

Hi all,

I've read all the various threads here about the Digistat +2 and the Honeywell T40, but I'm still stuck.

I want to replace our old T40 with the Digistat +2. The T40 has red/live coming in to terminal 1, blue/neutral into terminal 2 and black (assuming switched live) into terminal 3. This mechanical thermostat works and switches the heating on and off, but it's not timer, obviously. Hence, the Digistat +2.

Followng other threads here, I sleeved off the old (apparently-now-redundant) blue/neutral and put the red/live to the common terminal in the Digistat +2 and the black/switched live into the second terminal down (it's not marked as 'terminal 2' but simply 'On'). There is a third terminal, marked 'Off'. Either way, this is a simple switching circuit so far as I can tell, so apart from the correct on/off action, it should switch regardles of whether my black/switched live is connected to On or Off.

But it doesn't. No matter whether I connect my black cable to the On or Off terminal in the Digistat +2, it won't fire the CH (on a combi boiler that, remember, fires just fine when the T40 switches).

I've now removed the Digistat +2 and refitted the T40 and all is fine. I've tested the Digistat +2's switching capability with a battery and a bulb, and it works as I'd expect. So, my question is, why won't the Digistat +2 switch work to call for heat from my boiler? The circuit clearly completes, because I can get it to power a bulb. So I'm foxed now.

If it helps, the boiler is some brand that I've struggled to find information on online -- an Intensa.

Any ideas greatly appreciated.

Harry.

 

[tryingnottobeafool]

http://www.firexsafety.com/NR/rdonlyres/6FC43BA2-732F-4533-8534-52511DAD7CC8/0/DigistatPlus2.pdf


4 wiring programmes there, have you got combi?

what one have you got?

 

[hsabbers]

4 wiring programmes there, have you got combi?

Thanks... I already have those (it's the same instructions as came with the Digistat).

I have a combi boiler, an Intensa brand. There's no obvious model number on it that I can see, but the instructions (which we inherited when we bought this house) suggest it's either a TP23 or a TP30. But as I said, I've not been able to find any other useful information about it online.

Harry.

 

[tryingnottobeafool]

you need a 4 wire cable

red goes to live in

any wire to neutral

the other two wires to combi ' call' or 1 and 2 ( in boiler )

simpleset way is to look in boiler after disconnecting power and trace wires

or run another 3 strand cable back to boiler, if you have any lying about

use one from fused switch to thermostat/ timer and the other to boiler

 

[Minton]

Harry.

I can see five connections on the diagram for +2 but you seem to refer to only three.

Do you need to remove a cover to access the live incoming terminals?

 

[hsabbers]

Hi all,

Christmas kind of got in the way, so I put this project on hold. Anyway, thanks for these responses.

The Digistat +2 is a battery-powered stat and does *not* require a mains input (although it can be powered by mains, if desired, which is why those technical diagrams show a mains input in a dotted box, to indicate that it's an option). It is nothing more than a relay, and two AA batteries do the job of powering that relay. Indeed, it works -- I can hook the requisite terminals up to small lightbulb and have the +2 switch it on or off at will. So the switching circuit works. But it refuses to act as a call-for-heat switch, so I remain stumped. With the Honeywell T40 back in place, all works okay once more. But I really want to get rid of this simple mechanical switch and fit an electronic timer for better control -- it's not nice having to traipse downstairs at 6am in the freezing cold to twiddle the T40's knob.

Other threads on this same topic suggest that switching out the Honeywell T40 for a Digistat +2 is a simple case of live-in to the common terminal and the switched live to the 'On' terminal (which is the second one down on the +2). The neutral should then be sheathed. But this configuration does not work.

So, anyone else got any other ideas? All help greatly appreciated.

Harry.