Economy 7 - Hot water not working

Talldave

It would be a standard switch plate but with an additional cover that gives access to a fuse.

I would expect the MCB to be a 16A like the off peak circuit but I'm not a qualified electrician.  I'm sceptical of anything that looks botched, modified or out of place. And fitting a higher rated MCB to solve a frequent tripping problem is a typical botch (and isn't safe if the circuit is meant to be protected at 16A).

But we digress from your off peak problem!  Sadly I suspect you need to be debugging during E7 hours.

avoidtheupsidedownbottles

The setting you have on the thermostat is only about 30 or 35 degrees according to this

Gerry1

Get yourself a cheap neon screwdriver and touch it on the 'A' terminal after the meter has switched to cheap rate and see whether it lights up.  Or buy a cheap multimeter: search for '830B multimeter' (there are many similar brands, often yellow).  I've had one for decades, very good and reliable. Or take the plug off a table lamp and touch the wires across 'A' and 'B' and see whether it lights.

Whatever you do, don't touch any terminals, assume both are live at all times.  Similarly don't rely on the wires' colour coding or the circuit being off peak only.

MWT

Heely said:

New element.

That is the thermostat, not the heating element.

Sounds like your neighbour has replaced the thermostat which may or may not have been broken, but if the tank wasn't drained then he didn't replace the immersion heater itself...

avoidtheupsidedownbottles

Think the easiest thing to do first is to switch off Boost, and turn up the lower thermostat to 4.5 tonight and see if it works.

Talldave

OP was the tank drained down?

Gerry1

No, see 2:45pm post.  Or perhaps the neighbour just stood upside down instead...

avoidtheupsidedownbottles

The original t-stat was a Cotherm TSR with max setting of 160º C.  Replacement 'stat is a TSE with maximum of 70 as above.  Might account for the confusion with settings.  
Or the heater element may be knackered as well . .

Talldave

Gerry1 said:

No, see 2:45pm post.  Or perhaps the neighbour just stood upside down instead...

Sorry missed that in crossed postings. So the element's knackered then - simples!
I assume there is a cover that goes over that lower immersion element when we're not in diagnosis mode?

tim_p

MWT said:

Heely said:

New element.

That is the thermostat, not the heating element.

Sounds like your neighbour has replaced the thermostat which may or may not have been broken, but if the tank wasn't drained then he didn't replace the immersion heater itself...

That’s where I was going. Changing an element isn’t for the unwary. I think it was mentioned that it was changed in 2015 too. (Gonna tempt fate here but..) our element is 22 years old and in that time I’ve only replaced the stat once, I’m blaming that failure on ‘funny’ juice from the solar diverter.