One of our storage heaters, an Elnur SH24A, has stopped charging. It was new this year so I hope it's just the thermal cutout that's triggered (no idea why). Does anyone know how to reset one of these?

The only switch i've found that measures a high resistance (20 Ohms) accross it is a small beige cylinder with a little reddy-orange 'nipple' on it. The nipple is slightly moveable and I've tried tweaking it a bit (cue toilet humour) but the resistance stay stubbornly high. According to the wiring diagram, it is in the right place for the safety switch (Ts).

Any help greatly appreciated (and will save me about £350).