Honeywell Programmer

[someonelse]

Honeywell ST6400C

I had a brief power outage, and when power returned the controller did not reset properly

* the time display was blank
* both heating and Hot Water lights were permenantly on and did not respond to switching off or to timed on/of

Pressing the 'reset' button fixed things but involved re-setting time clocks etc.

User guide says there's a built-in battery that can handle outages up to 4 days (this was 5 minutes!) so I asume it's failed.

Can the battery be changed easily? Bought where? Need an electrician/technician or can I DIY and if so how?

Cheers

 

[vsn]

I've had this problem for a while and I've been waiting for some 'downtime' (e.g. warm weather) but yesterday it annoyed me so much that I swapped the battery on the spot.

You need a Varta Mempac 3.6V. This is a rechargeable NiMH battery. The one in my programmer was 100mAh, but technology seems to have progressed and new ones are 140mAh.

There are no screws on the programmer. Once you take it off the wall plate, it's all clips. There are two PCBs that plug into each other. It's quite simple to take apart.

Now the bad news: The battery is soldered onto the board. You will need a soldering iron. I also recommend a desoldering pump. It's soldered on both sides of the PCB but this being an old unit the PCB is not very dense. So if you can solder/desolder, it's a simple job.