Re: Immersion Heater Fuse Blowing

[MrCheerful]

Hope someone can advise.

> > The fuse on my immersion heater keeps blowing. It is on its own 15A > circuit. The fuse doesn't blow immediately but after one or two

days.

I have replaced the fuse three times and wired around the timer to > eliminate it as the cause. > > Could it be anything other than the immersion heater causing the blown > fuse ? > > The hot water is only heated by the immersion as there is no gas and > the unit is around 12 years old. The make is a Thermtec Ltd 3kw. > > If I need to replace the heater, do I need to buy a new thermostat or > can I re-use the old one ? > > Thanks in advance.

given the age, just get another immersion, these come with a new thermostat and only cost a few pounds.

MrCheerful

[MrCheerful]

Then to prove that the immersion is faulty, rewire it from a plug and see if that blows the fuse too. The thermostat will not cause fuse blowing in my experience, while the element will.

I have changed lots of elements over many years and only once has the cylinder started to twist and buckle because of tightness, although the element still undid ok and a new one went in ok. Always start the undoing process with the cylinder full, even if the element is at the bottom, the weight of water keeps everything stable, also use a socket with crossbar if possible. MrCheerful

[Andrew Gabriel]

The element could have shorted to the casing, causing it to draw more current. This will make the fuse carrier very hot (and the cable quite likely warm too). If it's an intermittent short such as a cable fault, then the fuse carrier won't have time to heat up (although it might be slightly warm just from normal operation of the immersion heater).

This is a handy technique to diagnose an overload current blowing a fuse verses a fault current (short circuit) blowing a fuse, but you have to get there immediately after it happens.

[IMM]

When removing an immersion element from a cylinder, always heat the copper around the immersion with a blowlamp. This expands the copper and makes it easier to screw out.