Backwards Room Stat

[DIYIdoit]

Hello Andy,

The wiring you quoted was there when we moved in, 3 wires from a 4 terminal stat probably was dangerous I don't know but I have changed the room stat for a non neutral one. It's still not earthed though only 2 wires coming from it to the programmer & the valve. 1 terminal on the new stat is not being used (Q12). Should it be? It's battery operated.

 

[CH4]

DIYIdoit,

The programmer's CH ON switch contacts probably welded together at the time the fuse blew, and terminal 4 has now become a permanent LIVE. This would be confirmed if terminal 2 (CH OFF) fails to become LIVE whenever the central heating is turned off at the programmer.

So, it appears that you may need a new programmer. Buying an identical model would mean that you could reuse the existing wall-plate and avoid any rewiring. LP522 programmers are frequently available on eBay for under £20, e.g. see THIS.

 

[DIYIdoit]

Cheers CH4, I'll wire no2 up ad see if it becomes live. Thanks for the link also, original cost me £60!!!

What does the d stand for in DHW?

 

[kevplumb]

Domestic

 

[DIYIdoit]

Ohhhhhh

Or in my case DOH!

Cheers dude

 

[stem]

It's possible, that if you've been blowing fuses, the programmer contacts have been carrying too much current and have become welded together and so permanently on.

 

[DIYIdoit]

Just to say a MASSIVE thanks for your help on this matter, I rewired the room stat as directed and fitted a new programmer (from eBay) this weekend and everything is A OK.

Cheers guys,

Pete.

 

[Razzler]

Can anyone help...My cylinder stat blew and took out the programmer.
On inspection it looks like a simple case of replacing LK7 (it sits on the PCB and is connected to the 'Live in' pin and is positioned next to RV1) which, although cooked, looks like it may have been a resistor.
Does anyone have any idea what LK7 is on the Honeywell ST6400 programmer and it's value please?
Many thanks...Razzler