"Jules" wrote in message
news

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



Residential electric water heater thermostats are on-off switches, and NEVER
send power to both heating elements simultaneously. When the water is cold,
the upper thermostat sends power to the upper element and heats the water at
the top of the tank. When the upper thermostat is satisfied, it disconnects
power to the upper element and sends it down to the lower thermostat, which
in turn sends it to the lower element, which remains on and heating, until
either the lower thermostat is satisfied, or the upper thermostat calls for
heat. Since you have some hot water, and you say that you have 240 volts at
the lower element terminals, I will deduce that the lower element is
defective. You can easily verify this with an ammeter