Thermostat for an immersion heater. It started playing up last weekend. I wasn't aware that the water heater had stopped working until Monday morning... whilst in the shower. Turning the temperature up to max made it just bearable. Certainly woke me up. There'd been sufficient hot water in the tank for me not to notice the slow cooling on the previous couple of days.

Too busy fixing stuff at work, and for other folk, to have time for a tinker with it during the week. Out with the testers, and after making sure the power was off, try and find the fault. So much simpler than some of the things I have to contend with at work. Element is okay, much to my relief - changing that would require the tank to be totally drained. Then there'd likely be a few tests to ensure a new one was totally sealed (he says, from past experience...). The thermostat, or stat, was open circuit, and the problem is located. About two minutes.

Was a bit late to go into town and buy a new one, as the electrical wholesalers all seem to close at about midday on Saturday. Just as well, as I discovered upon further investigation that there's a safety cut-out on this stat. A cut-out that could be reset.

Typical Engineer, had to have a look inside, and try to establish why the cut-out had operated. Fair amount of carbon around the area of the contacts, that possibly had been getting in the way of the movement. Cleaned out; put back together; and reconnected. Tested, and it seems okay. May take a bit of adjusting to get the water temperature just right. If it plays up again, I'll just replace it. They're not expensive, and this one is over twenty years old. I've had my monies worth...