Immersion Heater not working - is it just the Thermostat?

[reneel]

yes that is true, how silly am i!

whilst i'm being dumb, one last query, the thermostat obviously of course heats up and then heats the element by conduction which in turn then heats the water in the cylinder.

but what part does the element come into play regarding the immersion heater circuit... what i mean is, the circuit goes from LIVE to T to NEUTRAL terminals. If the element gets scaled up, etc how does this effect the resistance of the circuit... where is it linked exactly?

 

[Softus]

just to throw a spanner in the works - why can't a voltage test be used to test the element (from live to neutral)

Please define what you mean by a "voltage test".

I can't imagine anything safer or simpler than turning off the power to the element, testing for dead, then measuring the resistance.

If you've devised a new test that's safer, quicker and more accurate, then please let us know how to do it.

won't it do the same thing, ie show the element is working correctly?! please excuse me if i am way off it's been a looooong week!

How do you think a resistance test works?

 

[Softus]

the thermostat obviously of course heats up

Er, no. The heating it undergoes involves the subtle expansion of a bimetallic strip, which is imperceptible outside the thermostat.

but what part does the element come into play regarding the immersion heater circuit... what i mean is, the circuit goes from LIVE to T to NEUTRAL terminals.

The element is electrically insulated from the water. The element is itself coated with a conductive layer that heats the water,

If the element gets scaled up, etc how does this effect the resistance of the circuit.

It has no effect on the resistance of the element until either the conductive layer corrodes or the element burns out.

where is it linked exactly?

I'm beginning to wonder where you're linked.

 

[reneel]

a voltage test means seeing if there is voltage from one point or wire to another.

i am not sure about how a resistance test works - i suppose as you have mentioned before, by seeing if there is resistance between 2 points/wires.

 

[reneel]

i am sorry, i am confused now, been a looong week and am tired

but i really am interested now exactly howe an immersion heater works - the thermostat and element and the whole circuit. anywhere i can learn this from, any website(S)?

sorry for annoying you Softus, I'm not doing it on purpose and I'm not usually this stupid..

I did think that the rod-type thermostat was used though and not the bi-metallic strip type. but i'm not going to argue with an expert. sorry once again.

 

[Softus]

a voltage test means seeing if there is voltage from one point or wire to another.

So are you proposing to measure the voltage drop across the element, and calculate the resistance from that?

 

[reneel]

well i wondered if that could be done, just like measuring the voltage from the live to the thermostat terminals. i am thinking now that this will not work... feel so stupid.

 

[seco services]

after all that is the element ok or havn't you checked it yet ?

 

[Softus]

sorry for annoying you Softus, I'm not doing it on purpose and I'm not usually this stupid.

I'm not annoyed at all. I'm just baffled as to why you're trying to think of ways to not measure the resistance.

I did think that the rod-type thermostat was used though

The probe is indeed in the shape of a rod, hence the name.

and not the bi-metallic strip type.

If it doesn't have a bi-metalic strip, then how do you think it works?

i'm not going to argue with an expert.

I don't know why you think that I'm an expert, or that you shouldn't ask questions. I apologise if I've made you feel like that.

 

[reneel]

Sorry for all this confusion in my post! And my first post on this forum too!

Can we start again please and from your advice can you please explain to me the following/correct me where i am wrong (i would be so grateful for your help and for "educating me"!!) I am not usually this much of a dunce!

1) To test for a faulty thermostat in the heater, if there is no voltage from the LIVE to the T terminals this is proved?

2) To test for a faulty element, i test for resistance between the live and neutral terminals and if the resistance is more than 18-19 ohms (as worked out using the triangle) then the element has failed?

3) The heater works by the element being heated (from the live to the neutral, via the T terminal) and conducting its heat to the surrounding water.

4) when the temp is at it's setting (usually 60 degrees) the thermostat breaks the circuit and stops the element from heating

i appreciate your help and patience with me guys.

one last point - is an "INCALOY" element a lot better for "Hard water" areas, due to it taking longer to "corrode"?

Also I am sorry yes you are right, the rod is the shape of the thermostat, the metals bend and contract when heated/cooled (thus the bimetallic strip type)!

 

[Softus]

1) To test for a faulty thermostat in the heater, if there is no voltage from the LIVE to the T terminals this is proved?

Personally, I wouldn't do the live test - just a continuity test across the 'stat terminals.

2) To test for a faulty element, i test for resistance between the live and neutral terminals and if the resistance is more than 18-19 ohms (as worked out using the triangle) then the element has failed?

The resistance could be less.

3) The heater works by the element being heated (from the live to the neutral, via the T terminal) and conducting its heat to the surrounding water.

Yes. The heater works by being being heated.

4) when the temp is at it's setting (usually 60 degrees) the thermostat breaks the circuit and stops the element from heating

Yes, and yes.

one last point - is an "INCALOY" element a lot better for "Hard water" areas, due to it taking longer to "corrode"?

Yes, except that it's Incoloy - the other type is only used in Peruvian temples. The more Titanium, the better.

 

[reneel]

Thanks Softus. You're tops. I owe you a pint, or ten!! Oh just a continuity test (with power off) across L & T instead then.

OK so 18-19 ohms or a bit less is ok, but any more is a faulty element.

And yes sorry Incoloy!!! I was close

one last point?! what is the reason usually why the elemnt fails? is it a build up of limescale in the cylinder? and this of course causes more resistance / takes longer to heat up, if at all?!

 

[Gasguru]

The thermostat consists of a brass tube containing an Invar rod. The rod has a very low coefficient of expansion compared to the brass. As the water heats up the differential expansion between the two activates a switch.

IMHO Incaloy elements make little difference to longevity....I have yet to try titanium since they are not widely available and customers willing to spend the significant extra cost are few. As with many things it suits manufacturers to make poor quality elements...even Backer elements have only lasted 18 months

 

[Softus]

AFAIK all Incoloy variants contain some Titanium, but different recipes contain different ratios.

reneel, have you done the test yet?

 

[reneel]

done it, well the first part, again as you said with power off. no continuity between L and T. so i suppose the thermostat is stuck in the satisfied position and not opening.

so the thermostat has failed.