Excellent Controller and ideal retrofit for 6400 series.
I bought this to replace an existing ST 6400 controiller that had a failed back up battery.
Replacement took only a matter of minutes and required no skills, special tools or rewiring. This is because Honeywell have made the 9400 fit the older 6400 backplate. You leave the backplate in place.
You undo two captive screws at the base of the old unit.
You hinge up the old unit (it is held on two tabs at the top) and lift it off.
You fit the new unit over the tabs, hinge it down ands push into place and then tighten up the two screws.
Connecting pins on the rear make contact with the connectors on the backplate. That's all. It now works.
All that is required is to set the time and the programmes.
It is similar to the old 6400 but has a much clearer display and this is backlit (you can set it to be backlit or not). This is an excellent feature. It allows me to see the controller screen without needin a torch.
The programmer can be set to separately control the central heating and hot water circuits.
You can set multiple timed on/off periods for each day. Mine is set to 3 on/offs per day, but you can set the unit to operate differently if yoiu wish (in the master set up).
You can set the unit to be on a 1 week programe, where every day is the sam, or a 5/2 programme where weekdays and weekends are different or 7 individual days where each day can be different (a "copy" function makes this easy.. (This weekly, 5/2/ or daily option is in the master set up).
Buttons to allow an extra hour or override for the Heating and Hot Water are on the front. They are on opposite sides of the display, so you cannot accidentaly press the wrong one and they light up when activated.
The old controller had a slider for OFF/AUTO/ONCE/CONTINUOUS for heating and hot water. You had to open the cover to get to it. This one has a pair of push buttons and the display shows which one you have selected.
The original 6400C was a very good controller. This one is an imrpovement with the same functionality but extra features that are useful. For me, the bigger display and back illumination are the two best imnprovements.
It came with a new backplate.
If the electricity goes off (and it has) in a power cut, it has a back up battery and does not lose the time or the programme, so no work is needed.
HINT: if you are replacing an old controller, make sure that the two captive screws on the bottom of the existing back plate are fully undone. They are captive and cannot fall out. If you do not unscrew them enough they might stop the new controller slotting into place. If this happens then they need to be slackened off a bit more.
Great product from Honeywell that has stood the test of time and is now improved.
You can download all the information beforte you buy from the Honeywell website, but the information in the box is excellent.
Oh!, and it looks nice too!
Verified purchase: YesCondition: New