Hi Echo, thanks for your help, the light is not flickering its slightly glimmering, shows more in the dark, when on normal it's bright. I will send some photo's tomorrow of the stat front and back. I have had trouble finding installation details on it, I emailed ESi here are the messages. Hi Kevin, thank you very much for your help and the diagram. Can I be a pest and ask one more question. Everything is working fine but, I fitted an ESI 3 port mid position valve, works fine. I fitted an ESI room stat model ES-RTE/VF that works fine small blue light comes on with heat goes off when temperature reached, but if I turn the heating off at the programmer a (flomasta two-channel programmer model 25902X the blue light on the room stat glimmers. I have checked all the wiring to the “Y” plan all correct. I am now wondering if the room stat is now faulty ??. Can you help please. Reply The only time I have seen this before was when the Live and Neutral supplies were reversed. If the Programmer is off there can be no live supply to the Thermostat, probably worth checking the Live and Neutral connections. My reply Hi Kevin, thank you for the quick reply, I have checked the wires to the room stat, blue negative from N in stat back plate to all the negatives in the wiring centre number 2. L has a loop to number 1 in the back plate Brown is in number 1 to number 4 in the wiring centre nothing in number 2 and a black wire from number 3 to number 5 in the wiring centre. Still got a glimmering blue light. Sorry to be such a pain. Reply As you will appreciate it is difficult to diagnose these things at a distance. I still suspect there is a wiring issue, as I mentioned when the Programmer is off there should be no live supply to the Thermostat (therefore no power to illuminate the Neon. So, I suspect there is a back-feed on the Neutral. Have you checked for a Voltage across the Neutral to Earth? Or when disconnected from the Switch Live to Earth? . Hope these will make more sense to you than they did to me.