Just wanted to confirm that the problem relay is the one I marked in green circle (picture attached). It's next to R/BK P26-2 connector. Thanks.

Potter and brumfield...$3.93

https://www.newark.com/potter-brumf...rt334024f/relay-spst-no-250vac-16a/dp/17C6470

 

Now that I look closely, I am not sure that's the right relay though. I have to figure out a way to correctly trace the relay on back of circuit board. But, It seems it could be the one in the corner - T90S1D42-24 marked in green (new pics attached). I see soldering has come out from one of the pin on that one.

 

Yes looks like soldering needed, Farnells fo them, check part number in your country...
Ideally check there is 24V dc on the coil pcb terminals..

https://uk.farnell.com/potter-brumf...d42-24/relay-spst-240vac-28vdc-30a/dp/1838951

 

So, soldering did the trick. It was loose relay terminal causing the problem. Relay itself was good.

Dodgydave - Appreciate your help, you have been great!!