Chosen Solution
The fix I concluded that the boil-dry cut-out was faulty. On disassembly I found it was a standard resettable thermal cut-out except that it was studded. Here it is mounted on the main heater with the reset button extension attached (the brown ring is the keep-warm heater):
dismounted:
and the heater with the thermostate dismounted:
I couldn’t find any studded thermal cut-outs online but the supplier’s website gave an exploded diagram and parts list (https://media.nisbets.com/asset/en/media…) I ordered the Dry Heat Thermostat and Layer for Thermostat (parts 19 and 20). I couldn’t quite see what the Layer was but thought I’d better order that too. It took 3 months for the parts to come from China, but the replacement thermostat wasn’t studded! Here are the old and new, side by side:
This threw me, but after sleeping on the problem I realised that the thermostat could be screwed onto the Layer, and I just needed a M4x10mm screw to attach the Layer to the heater. Here is the thermostat mounted on the Layer:
Searching online it appeared that other people had experienced the same fault, in fact one person had sent their first percolator back and had the same problem with the replacement! I concluded therefore that this was a known fault and a design change had replaced the studded thermostat with a convention one plus the Layer. This would somewhat reduce the heat conductivity to the thermostat, preventing premature operation.
