Hmm, our water heater seems to have become unwell in the last couple of days - taking a long time to reheat, and whilst the hot water it eventually produces is still hot (not just warm) it runs out very quickly.
It's a dual-element design, and having just run the tank cold, with a meter I'm getting 240V at the lower element terminals but nothing at the top one, suggesting the upper thermostat's at fault (I'll rule out wiring too in a few minutes, just to make sure it's not a loose terminal or something silly).
Questions:
1) Just to clarify, should the upper 'stat / element be operating with a fully-cold tank? I assume both elements should be running in that situation, but figured I'd check.2) Do these thermostats change resistance according to temp, or are they either off or on depending on setting? (I'm just wondering if I can somehow test it in isolation by blasting it with a hairdrier, or something, and measuring resistance across the terminals, but maybe that won't get it hot enough to prove anything)
3) The upper 'stat is a WH-10 7-terminal, but it's a non-adjustable one (says as much on it, along with something like "factory pre-set to hot setting"). I can get a replacement WH-10 easily enough, but I've only seen adjustable ones for sale - presumably I can just drop one of those in, except that I've no idea what the manufacturer's idea of "hot setting" is :-)cheers
Jules