Problem when I replace Satchwell TLX2259 for Sunvic TLX-9201

[G0AV0]

My problem is LED indicator is not working - I have tried a second unit, and get a brief flicker when thermostat switches on central heating.
I enclose image of the old thermostat wiring in my album.

The wiring to my new Sunvic is:

Blue to terminal 4 (neutral)
Brown to terminal 1 (common)
Earth wire coded with white tape to terminal 3 (demand)
(The earth is NOT being used as an earth, but as a switched live.)

I was considering swapping the brown & blue around, but reluctant in case I blow a fuse. I thought there might be a diode in circuit acting as a switch, but wrong polarity/wiring diode might not be passing current to indicator led - I thought it unlikely that I might have two faulty thermostats.
Can anyone help please. Thanks.[/img]

 

[doitall]

Perhaps you should post what the old numbers/colours were, before the big bang.

 

[D_Hailsham]

The wiring to my new Sunvic is:

Blue to terminal 4 (neutral)
Brown to terminal 1 (common)
Earth wire coded with white tape to terminal 3 (demand)
(The earth is NOT being used as an earth, but as a switched live.)

That's correct!

 

[mikely]

If the thermostat is operating the heating system but not the led, it would suggest that you have no connection to neutral at the thermostat.