Economy 7 cylinder - top immersion heater not functioning

[willcross]

Hi DIYnot, hope you can help

Recently moved into a flat with an economy 7 cylinder
with 2 heaters in it.

The bottom heater of the 2 is the one that runs with economy 7 power at night - this one is working fine.

But the top one (which should be providing on demand water heating at any point right?) doesn't heat the water up when i turn it on.

e.g. yesterday i used up pretty much all the hot water stored up from the night before. and then turned on the 2nd switch (on the left in photo). Even after waiting for a few hours, water is cold.


I don't think its the fuse that has blown as the switch in question on my switchboard hadn't tripped.

What's my next move?

Thanks in advance

 

[just pumps]

Couldn`t help but notice there are no screws in the switched fuse spur, do you know why not? Start by trying another fuse as that type doesn`t showing signs of failing externally or with it switched off remove the nut and Silver cover and see if the wires are connected or if there are signs of burnt wires under the cover. Depending on the your skill level you could also check the wires behind the fused spur and the round Silver cover with a test meter.

 

[oldbuffer]

1. The fuse can blow without tripping the switchboard circuit breaker. You need to test the fuse. Multimeter is best, otherwise just try it in a light or similar which you know to be working. Do not leave immersion heater fuse in light plug, put the original back. (Should be a 3A or 5a)
2. Only if your completely confident you can turn off the power to the top immersion heater:
2a. Isolate power.
2b. Remove metal cover.
2c. Check wiring inside. Given what looks like burn marks on insulation above cap, I suspect there may have been electrical arcing inside the cap. If the insulation on any of the wires is burnt / hardened, call an electrician unless you are really competent with electrics. If wires are damaged, see if you can cut back and re-strip insulation and re-make connections exactly as at present.
2d. If / once wiring OK, see if there is a thermostat reset button. This will be a small, normally red or black, plastic button about 3mm in diameter. It may be recessed. If there is a reset button, press it and you may feel feel it "click". If you do it means the water has overheated at some stage and the safety thermostat has operated. Pushing the button will have reset it, and the immersion should work again.
2e. Beyond the above you need a multi-meter, when you can:
2e i) Check that the resistance of the element is around 18 ohms. If zero or much more than 18, then the element has gone and will need to be replaced.
2e ii) Check that the thermostat (not the re-settable one referred to above, the one which has an adjustment dial) goes open circuit above the set temperature, and short circuit below the set temperature. If the thermostat isn't working it will need to be replaced. No wet work involved as its sits in a pocket in the body of the immersion heater. Buy a new thermostat the same length as the old and wire it in like for like.

I'll stress again that if you aren't confident working with mains voltage electricity, get someone who is. You can kill yourself making a mistake.