I have it going again after swapping out 4 triacs. The fifth T4 burnt the pub and traces so I just won’t use it.
Also the 0.5A fuse went. These are nasty little devices because they have high wire resistance which can cause issues with input resistance to linear supplies. Also the fuse wire to fuse end terminal can go high resistance and cause intermittent grief.
I am also surprised that I had three triacs go before this. I note that the triac is rated for 0.8ARMS. (BT1308W-600D). My AC vales have a dc resistance of ~25 ohms. Impedance will be a little higher at 50Hz but I have a nice solid 24vac supply that takes the RMS on current to over 0.8A. No wonder they are dying!