Drayton Digistat 1 not turning the CH OFF

I have a Wired Drayton Digistat 1 which is battery operated (2 cells).
The Programmer is a Honeywell 6400C with 3 On/Off and 7 day setting and the Boiler is a Potterton Suprima.
There is a Mid Position 3 port Valve.

When the CH is ON through Programmer), the Boiler runs irrespective of what the Thermostat setting is (even if the setting is lower than the room temp).
This is a new house we have moved in, so can't tell if it ever worked or stopped working recently.

I opened the Programmer and checked the connections.
Apart from the Ground, it has 5 wires connected :
Live, Neutral, HW ON, HW OFF, CH ON
Note that the CH OFF is not connected (and the manual says that is a valid connection for Y Plan). My local CH Engineer said that the CH OFF is never connected.

I suspect the Thermostat is wired wrongly.
I checked the suggested Elecrical Connections for a Drayton Digistat 1 and it says :
1 - Common, 2 - Satisfied and 3 - Demand.
However, on mine, 2 is not connected.
Only 1 (red) and 3 (yellow) are connected.
On the wall, there is a note listing the old Honeywell connections :
1 - red, 2 - blue, 3 - yellow, 4 - stat, earth

Do I need a wire going to 2 ? If so, which one ?

Any help / advice highly solicited.

By the way, I can hear the stat click when I set the temp above or below the room temp - which suggests that the relay is working.
I replaced the batteries.
Before I replaced them, it had another problem (in addition to the existing one) : when the CH was OFF, the Boiler could be turned OFF or ON by changing the stat setting !

Programmer and roomstat have wires connected to the correct terminals, however I can not say that it is all wired correctly, sounds as though it isn't.
Has changing the batteries solved the problem mentioned in your second post?

Thanks Mick.
Yes, changing the batteries seem to have solved the 2nd problem. Or it might be the tweaking that has actually sorted it as it is a bit strange for a low battery stat to turn the Boiler On / Off when the Programmer is OFF !

Yesterday when I tried putting the CH and HW to Constant (at the Programmer - to test if the Valve rotates), the problem appeared to have come back briefly (I mean the Boiler turned ON when both CH & HW was OFF) until I turned down the stat and since then it is behaving (I mean that the stat is not turning the Boiler ON when the CH / HW is OFF).

When I put the CH to Constant, the red dial on the Valve turned one and three-fourths of a turn - just about 10 mins (comparing with a clock) short of the flat position (mid position).
When I put the HW to constant, it turned by another 20 mins roughly (again comparing to a clock hand).
At least, it moves - so can assume that it is not stuck.

Regards

rojroj said:

When I put the CH to Constant, the red dial on the Valve turned one and three-fourths of a turn - just about 10 mins (comparing with a clock) short of the flat position (mid position).
When I put the HW to constant, it turned by another 20 mins roughly (again comparing to a clock hand).

Click to expand...

Sounds like a Sunvic Unishare valve. Does the actuator (box on top) have the number SDM 1901? If so it is a MoMo valve (motor on, motor off), which do not have a good reputation for reliability. In fact all Sunvic valves have a poor reputation - see Sunvic motorized valve failures.

Although they can be repaired, it is probably better, in the long run, to change it for a Honeywell V4073.

The old Digistat is very confusing when the batteries go. There are 2 batteries, each one has a different function. I think one runs the clock and display while the other drives the relay. Otherwise it was a great product.

twgas said:

Programmer and roomstat have wires connected to the correct terminals, however I can not say that it is all wired correctly, sounds as though it isn't.
Has changing the batteries solved the problem mentioned in your second post?

Click to expand...

I made this statement assuming you had a Yplan with a honeywell (or similar) valve. the Sunvic system uses relay box and is wired differently.

Yes the number SDM 1901 is present.
I think you are right about the Valve problem.
I get all sorts of problems - sometimes the stat controls the bolier (according to the set temp) even when the Programmer is OFF.
Again, at other times, when the Programmer is ON, the stat is totally ignored and the boiler is ON all the time.

Thanks for your help - much appreciated.