Wiring check for thermostat

erergwerg · Jun 2, 2022

Hello,

I have a piece of equipment with a thermostat attached to the bottom to heat a tank. This has stopped working- the red light does not turn on and it no longer heats up. The thermostat still clicks when twisted. I have attached a photo - I have used a voltage tester to test if electricity is running. It is running up the white wire but then there's nothing on the wires leaving the box (circled in the photo). Any idea what has gone wrong? does one of the boxes need replacing? I have a similar device and there seems to be extra wires connected to the the two metal pieces sticking out from the top box so I'm not sure if the wiring is correct for this one?

Thanks in advance

littlespark · Jun 3, 2022

First of all, the entry holes for all the cables need sorted out before you attempt the wiring.

There should be something attached to the top connections, but the fact that there isn’t makes it look like they have been disconnected deliberately by you or someone else.

AT A GUESS and by that I mean you need to check with any wiring diagram that came with the equipment…. The yellow crimp you can see needs taken off where it is and moved onto one of the top terminals…. Then a link, crimped at both ends between the other top terminal, and the one you took the yellow from.

The live feed comes in the side, through the thermostat at the top, then through the safety thermostat at the bottom… out the bottom hole to whatever heating load.
The black wires go to an indicator light, and wired in parallel across the load.

The fact that it looks to have been disconnected suggests top thermostat doesn’t work and has been bypassed. It can be checked with a multimeter if need be.

Avo Mk8 · Jun 3, 2022

As per littlespark. The top adjustable thermostat should have been in circuit.
Removing it has put the burden of switching onto what appears to be the safety cutout below, which may not be designed for that role. I suspect the bottom unit needs to be replaced, but given it's the safety device, you need to be absolutely sure to get the correct replacement.

Even if the top thermostat does work, that doesn't help you get it going if the bottom one is broken.

And another guess - maybe there was a change in the process the tank was being used for, and the tank didn't get quite hot enough, so the top thermostat was taken out of circuit, relying on the lower one for control, without thinking about the consequences!