I connected live (brown) to A and 3 (grey) to B, leaving the other two wires unconnected. When doing this the heating runs constantly no matter what temperature is on the thermostat.
That seems correct.
The black wire needs to be safely terminated in a block connector or similar and is not used with the battery powered thermostat.
I would temporary put grey in a terminal block to test the heating goes off.
as the old one always overheats the house.
Question is was the old thermostat faulty, or was there some other fault?
I had mothers house getting too hot, and first attempt was change wall thermostat, I used a cheap programmable wireless unit
it was a failure, and I was not inclined to make the same mistake twice, for fitted better heats on the TRV's,
they did work well, with a modulating boiler, but new owners did not want them so changed back to standard, and now the lock shield valve had be set, which was easier when I had a computer report of target and current temperatures
.
So even if the wall thermostat is faulty, the home should not over heat. The boiler will cycle a lot and waste energy, but home should not over heat.
Unless that is if you live in an open plan house or have a hot air boiler so no TRV heads fitted.
Analogue and Digital can refer to human machine interface (HMI) or the electrics/electronics, in the main analogue is better, but often the boiler will not allow use of analogue controls. The whole idea of the digital thermostat it to turn off the boiler in warm weather, it is not to control room temperature, the TRV does that.
The problem is a radiator has two controls, the TRV and the lock shield valve, and mechanical TRV heads are marked *123456 not °C which is a bit useless, so without a differential thermometer to set the lock shield valve it is guess work which unit needs altering. With an electronic TRV head
even a cheap one as shown here, I paid £15 each for these blue tooth heads, you can actually set the temperature in °C so if too hot you know the lock shield valve open too much.
The TRV takes time to open and close, around 3.5 minutes to do the exercise once a week Saturday at 12 noon to stop the valve sticking, and unless the lock shield valve is set in 3.5 minutes the radiator can get stinking hot, and this can initiate a hysteresis where the TRV closes and opens to try an control the temperature but keeps over shooting.
