On Tue, 8 Oct 2019 22:10:21 +0100, Gareth's was W7 now W10 Downstairs Computer
wrote:

the few mV from a thermocouple being IMHO too feeble to operate
a mechanical valve.

Naah, it's the current that creates the magnetic field.

Check the thermocouple is getting hot, possibly by using an external gas torch.

Thomas Prufer