Digistat 3 Wiring

[ferrari2005]

I'm very confused - not hard I suppose

I'm replacing a Danfoss RMT 230 with a Digistat 3.

The Danfoss had 3 wires connected:
1) Red to contact 1
2) Yellow to contact 2
3) Blue to 4

According to Danfoss, contact 1 is Live, 2 is Call and 4 is N (common?)

When I connect the Digistat like:

Red to contact 1 (I think red is Live)
Yellow to Contact 3 (I think Yellow is Call)
Blue taped off.

The boiler starts the central heating ignoring the fact that the digistat is not calling for heat (temp set to 5 degrees) and also the main programmer is set to off for both HW and CH.

The boiler is a Vaillant Thermocompact 620E

What am I doing wrong?

This is not the first time I've replaced with Digistat 3's.

 

[gas4you]

You seem to have got the wires correct. Although I wouldn't call neutral common! It is Neutral. Common is refered to the switched live going to the digistst 3 what you are calling 1.

So the digistat 3 should be live in = common, heating demand = 3.

If this is what you have done then try connecting return to boiler on 2 as an elimination experiment.

As you rightly say, no neutral and earth required on this model.

Then if still doesn't work remember rule 1. Just because it is new doesn't make it NOT faulty

 

[Softus]

Don't you have multimeter with which you can test the switched live from the 'stat?

 

[Heating Boy]

and also the main programmer is set to off for both HW and CH.

Unlikely to be the Digistat 3 unless the programmer has gone aswell - as the live to the thermostat comes from the programmer - so no live to the thermostat = no live for the thermostat to send to the MV.

Is it a S-Plan system by any chance? If so I'm guessing a stuck microswitch in the M.V. head.

 

[Softus]

Is it a S-Plan system by any chance? If so I'm guessing a stuck microswitch in the M.V. head.

Why would you want to be "guessing"?

 

[gas4you]

also the main programmer is set to off for both HW and CH.

Missed this bit first time

Check 2 port or 3 port valve as heating boy points out and as softus says with a multimeter preferably

 

[ferrari2005]

Don't you have multimeter with which you can test the switched live from the 'stat?

Hi,

I put a continuity tester across terminals 1 & 3 on the digistat 3. Is it normal that I get a signal even though the thermostat is set to low?

Using the multimeter, how would I test further?

cheers

 

[gas4you]

Was this done with the cables disconnected and an actual continuity test or do you mean with 240v test.

If the first then no you shouldn't get continuity. Have you tried across 1 & 2?

is tterminal 1 , common, live all the time, even when programmer is off for ch?