Thermostat kaput

karl-123

removing and re-installing programmers can be tricky as they are
all made of cheap plastic,and have differently positioned clips to
release them,and the contacts, become fast/stuck over time,
they need gentle manipulation to become free,
i carry thin strips of fine blue sandpaper very usefull for cleaning contacts,

good luck ......

ps. do not try removing the programmer and installing pieces of wire as links,
to get you ch/hw working
unless you have studied the wiring diagrams,
and you know for * sure *
your boiler needs 240v switched live
" incoming " :mad:

kizkiz

I'be already popped the top off and had a good look. It came off very easily. All looks pretty normal inside as far as I can tell.
As said, from googling there doesn't appear to be a replaceable battery.
Nothing is now working. No hot water or heating, so its not just the lcd display.

From reading, and as others have mentioned, I can pick up a st9400a as a straight replacement. It seems to use the same back plate.
Is it just as simple as popping the new unit on to the current plate and wiring or will I need to get it rewired?
Ta

kizkiz

Oh and I'll have a look at cleaning the contacts in the morning first

Myser

If you do decide to clean the contacts on the wall plate as well, ensure the central heating controls main supply switch is off!

Some of the contacts on the wall plate may be live.

kizkiz

Myser wrote: »

If you do decide to clean the contacts on the wall plate as well, ensure the central heating controls main supply switch is off!

Some of the contacts on the wall plate may be live.

Yup, i'd worked that one out, but always worth posting for others reading :T

kizkiz

Swapped the old one for a ST9400A and all is working again.
Such a simple job in the end.