Element in the water tank - what does it do?

[NewOrder]

Not sure if this in the right place, but I am asking this from a wiring perspective rather than plumbing.

We have a standard Honeywell timer (early 80's vintage) and there is a 1.5mm flex going into an element in the hot water tank. Am I right in assuming this a backup if the boiler fails we still have hot water? Because I tried once when the pilot light went out and we had no hot water at all.

So what is the element for?

The water tank was put in at the same time as the central heating.

Another thread on here (the one with the fuse blowing in the shower) reminded me to ask this, it is something I have been meaning to ask for ages but kept forgetting as its not really a problem.

 

[OwainDIYer]

We have a standard Honeywell timer (early 80's vintage) and there is a 1.5mm flex going into an element in the hot water tank. Am I right in assuming this a backup if the boiler fails we still have hot water? Because I tried once when the pilot light went out and we had no hot water at all.

So what is the element for?

Are you sure it's an element? It might be a thermostat.

http://www.discountedheating.co.uk/shop/acatalog/What_is_a_cylinder_thermostat.html

http://www.screwfix.com/p/dual-safety-thermostat-7/21275

 

[seco services]

As you say a backup for when/if the boiler fails.

If it's not working and has never been used since installed more likely the elements failed.

 

[EFLImpudence]

A picture would save a lot of guessing.

 

[xr4x4]

Is it one of these ?

 

[NewOrder]

It looks like that, only its silver and there is no writing or switch on it.

 

[Taylortwocities]

So, its an immersion heater.

As you have guessed, its there to heat the water in the tank. You'll only use yours if the boiler fails.

It's a good idea to test its working from time to time.

 

[NewOrder]

That is the problem, when I did test it a few years ago it didn't work. But I wasn't 100% sure it was an element so didn't investigate further. However around ten years ago we were unable to have the heating on water on at the same time, before that we could, so I suspect that is apart of the same fault?

Can I test the element by measuring its resistance?

 

[333rocky333]

Yes you can, safely isolate the power first though, also check there is no continuity between the element and earth.

The element is usuallly 3000 watt, guessing the voltage at about 240 volt, then using ohms law you will know the resistance.

 

[JohnW2]

The element is usuallly 3000 watt, guessing the voltage at about 240 volt, then using ohms law you will know the resistance.

.. but be aware of the fact that, if 'cold', the element's resistance could be a fair bit less than the Ohm's law calculation will suggest; even if the water in the cylinder is hot, the element is unlikely to be as hot as when it's actually being electrically heated.

Kind Regards, John.

 

[JohnD]

If it was me I would start by testing that it has power to it. You need to do that anyway to make sure that you have safely isolated it before starting work.

The thermostats also fail.

Changing an old element can be very difficult as they corrode into place.

 

[Lectrician]

Even an element that has never been used can corrode and fail.

I would not just try measuring the end to end resistance, I would want to measure from L/N to earth with an insulationg tester ideally.

Turning the double pole switch off before the element and testing to the elements terminals under the metal cover is all thats needed.

 

[Taylortwocities]

Bear in mind that, if the tank is full og hot water, the thermostat may be open and not closed.

 

[DetlefSchmitz]

Another possibility is that the thermostat over-temperature trip has gone and needs resetting. That would be a reset button under that cover. (Isolate first though!)

This is a common problem these days with alternative water heating sources.

 

[wingcoax]

A bit of a daft question, BUT do you have two switches on the supply? Some were installed with a switch in the kitchen(or other place) downstairs and one upstairs near the tank.