Immersion heater circuit keeps blowing

[Mr Grieves]

Hi all,

I am having some problems with my immersion heater. There are two heating elements one at the top and one at the bottom of the boiler. When you switch the top element on at the switch it starts to work immediately. The bottom element is on a timer and turns itself on around midnight every night (although I dont know where the timer is??, possibly an Economy7 system??)

The problem is every night when the bottom heater turns itself on the circuit breaks at the main fuse box. I'm not sure what is causing this and was hoping that someone might know. I've check the heating element and it looks fine. I've also replaced the wire from the element to the switch unit. Also I changed the switch unit about six months ago and this sorted the problem out for a while but the same thing has happened again in the last few weeks.

Any suggestions???

 

[PEDANTICVINDICTIVEMAN]

Disconnect the wires to the bottom element and make safe, see if it blows the fuse when the power is switched on to it, if it does you wil have to find where the fault is, if not then it proves the element is nacked and replace with a new one.

 

[Malc]

Do you mean the MCB trips i.e. the "fuse", or the main breaker which is could be a RCD in which it will have a figure of 30mA or 100mA on it.

Why do you think the element is ok?

Are you sure that both top and bottom elements are not coming on together?

 

[oilman]

How old is the element? If it's over five years and you use economy seven, it's done a lot of work and you're on borrowed time. Don't mess about, change it.

 

[kevplumb]

economy 7 ???

 

[bathjobby]

Echo the others, how do you know the bottom element is ok ? Suggest you disconnect it and put a meter on it and check it isn't earthed. Are you in a hard water area ? Have seen lower portions of tanks in hard water areas fill with deposits and cover the lower elements causing them to overheat and eventually blow (literally break open) causing a circuit to earth through the water.

 

[Mr Grieves]

Don't know if the element is ok but I removed it and it is not cracked. Also not sure if I live in a hard water area (i live in south london so probably). The element is at least three years old and probably more. I'm certain that both the elemnts are not coming on at the same time because one is on a timer and the other isn't. It is the circuit breaker in the fuse box that blows.

I was thinking I could swap the top and bottom elements around and see if the fuse still blows. As you can probably tell, I'm no expert so advice is much appreciated.

 

[Bahco]

The fuse goes when power comes on to appliance so could be a short circuit somewhere. Have you hammered any nails into the wall lately?
Would try PVmans suggestion first as this will tell you if the element or wiring is faulty.