Welcome to the forum. Although you can post in any forum, the USA forum is here in case of local regs or laws
Try turning it up to 90, see if it moves, if not, I’d say one of them is faulty.
Reply to the thread, titled "Thermostat on burner low but temp indivator much higher" which is posted in UK Plumbers Forums on Plumbers Forums.
We recommend City Plumbing Supplies, BES, and Plumbing Superstore for all plumbing supplies.