[Diabolical Artificer]

Thanks both. Re zeners, or avalance type diodes, I wonder if a PTC thermistor or maybe an LED and LDR would serve to adjust for temp? I know you can get better voltage references but there are non I'm aware of that'll do a few hundred volts. Having said all that it's probably best to use gas valve VR in combo with SS regulation. Probably talking out of my hat, just pondering.

I'll keep dipping into this subject and do some more testing etc when the chance occurs., Andy.