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Default Immersion Heater

Hi

I need to check a 3kw x 27" immersion heater element to see if it's working.
If I connect my multi meter across the terminals, what resistance should I
find?


--
Dave
The Medway Handyman
www.medwayhandyman.co.uk
01634 717930
07850 597257


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HI Dave

On Sun, 21 Jan 2007 20:43:51 -0000, "The Medway Handyman"
wrote:

Hi

I need to check a 3kw x 27" immersion heater element to see if it's working.
If I connect my multi meter across the terminals, what resistance should I
find?


Something lowish (in the region of tens of ohms) - but greater than a
short-circuit (zero resistance).

If you've got a failure then it's as likely to be the thermostat (can
be tested using the meter and 'tweaking' the dial until it opens or
closes - while disconnected from the mains supply, of course...

Alternatively - wire a mains lightbulb across the heater element and
reconnect the mains. If the lamp lights, but you don't get any heat
from the immersion then it's the element at fault...



Hope this helps
Adrian
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"The Medway Handyman" wrote in
message ...
Hi

I need to check a 3kw x 27" immersion heater element to see if it's

working.
If I connect my multi meter across the terminals, what resistance

should I
find?


--
Dave
The Medway Handyman
www.medwayhandyman.co.uk
01634 717930
07850 597257



IME immersion heaters tend to fail as the sheath gets punctured
usually due to a build up of calcium deposits, and the first signs are
not a change in resistance of the element, but rather an increase in
leakage current. Isolate both terminals of the element, check that
there is a lowish (10's of ohms) resistance between them, and also a
very high (megohms) resistance from the copper tank to the two
terminals. I have some flats where electric immersion heaters are the
only hot water source, and they don't last very long at all, even the
better ones intended for hard water regions.

AWEM


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"Andrew Mawson" wrote in message
...

"The Medway Handyman" wrote in
message ...
Hi

I need to check a 3kw x 27" immersion heater element to see if it's

working.
If I connect my multi meter across the terminals, what resistance

should I
find?


--
Dave
The Medway Handyman
www.medwayhandyman.co.uk
01634 717930
07850 597257



IME immersion heaters tend to fail as the sheath gets punctured
usually due to a build up of calcium deposits, and the first signs are
not a change in resistance of the element, but rather an increase in
leakage current. Isolate both terminals of the element, check that
there is a lowish (10's of ohms) resistance between them, and also a
very high (megohms) resistance from the copper tank to the two
terminals. I have some flats where electric immersion heaters are the
only hot water source, and they don't last very long at all, even the
better ones intended for hard water regions.

AWEM



Andrew, Have you tried the ones with stainless steel jackets. They should be
a lot more resistant (to corrosion that is).

Regards

Bob


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Default Immersion Heater

On Sun, 21 Jan 2007 20:43:51 +0000, The Medway Handyman wrote:

Hi

I need to check a 3kw x 27" immersion heater element to see if it's working.
If I connect my multi meter across the terminals, what resistance should I
find?



A little under 20 Ohms.



--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards


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Default Immersion Heater

The Medway Handyman wrote:
Hi

I need to check a 3kw x 27" immersion heater element to see if it's
working. If I connect my multi meter across the terminals, what
resistance should I find?


Why bother? - sling it in the skip and fit a new one which will cost about
£20 - the customer will be happier and you won't be back there working for
free every weekend trying to get it to work.


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"Bob Minchin" wrote in message
...

"Andrew Mawson" wrote in

message
...

"The Medway Handyman" wrote in
message ...
Hi

I need to check a 3kw x 27" immersion heater element to see if

it's
working.
If I connect my multi meter across the terminals, what

resistance
should I
find?


--
Dave
The Medway Handyman
www.medwayhandyman.co.uk
01634 717930
07850 597257



IME immersion heaters tend to fail as the sheath gets punctured
usually due to a build up of calcium deposits, and the first signs

are
not a change in resistance of the element, but rather an increase

in
leakage current. Isolate both terminals of the element, check that
there is a lowish (10's of ohms) resistance between them, and also

a
very high (megohms) resistance from the copper tank to the two
terminals. I have some flats where electric immersion heaters are

the
only hot water source, and they don't last very long at all, even

the
better ones intended for hard water regions.

AWEM



Andrew, Have you tried the ones with stainless steel jackets. They

should be
a lot more resistant (to corrosion that is).

Regards

Bob



Yes Bob, that's what's been in for the last 8 months with fingers
crossed !

AWEM


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The Medway Handyman wrote:

Hi

I need to check a 3kw x 27" immersion heater element to see if it's working.
If I connect my multi meter across the terminals, what resistance should I
find?


L-N around 20 ohms, but it may be less.
L-E should be o/c, if it conducts its electrically leaky and will pop
an RCD - but will work fine for a bit on a non-rcd supply, assuming a
decent earth connection. No decent earth and you'll really have a
problem.


NT

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Ohm's Law
http://www.grc.nasa.gov/WWW/K-12/Sam...w/ohmslaw.html

Nice to keep for further reference

pete

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Phil L wrote:
The Medway Handyman wrote:
Hi

I need to check a 3kw x 27" immersion heater element to see if it's
working. If I connect my multi meter across the terminals, what
resistance should I find?


Why bother? - sling it in the skip and fit a new one which will cost
about £20 - the customer will be happier and you won't be back there
working for free every weekend trying to get it to work.


It's one I fitted about 6 months ago. Got it from Toolstation. I suspect
it's the timer at fault because he has hot water OK in the mornings, but not
later on in the day.

I need to isolate the problem.


--
Dave
The Medway Handyman
www.medwayhandyman.co.uk
01634 717930
07850 597257




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Default Immersion Heater


I need to check a 3kw x 27" immersion heater element to see if it's
working.
If I connect my multi meter across the terminals, what resistance should I
find?


The power dissipated in a resistive element is :-

Power = ( V * V ) / R, so transposing the equation we get R = ( V * V ) / P.

So, if the mains voltage is 240V and the power is 3KW the resistance should
be

(240 * 240) / 3000 = 19.2 ohms.

I have done a quick check on this using my electric kettle, which incidently
is 2.4KW , and reads 25 ohms on my multimeter, near enough ?

Ian.


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In message , The Medway Handyman
writes
Phil L wrote:
The Medway Handyman wrote:
Hi

I need to check a 3kw x 27" immersion heater element to see if it's
working. If I connect my multi meter across the terminals, what
resistance should I find?


Why bother? - sling it in the skip and fit a new one which will cost
about £20 - the customer will be happier and you won't be back there
working for free every weekend trying to get it to work.


It's one I fitted about 6 months ago. Got it from Toolstation. I suspect
it's the timer at fault because he has hot water OK in the mornings, but not
later on in the day.

I need to isolate the problem.

So shouldn't you check that the element is actually getting volts when
the timer claims to be on ?

--
geoff
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raden wrote:
In message , The Medway
Handyman writes
Phil L wrote:
The Medway Handyman wrote:
Hi

I need to check a 3kw x 27" immersion heater element to see if it's
working. If I connect my multi meter across the terminals, what
resistance should I find?

Why bother? - sling it in the skip and fit a new one which will cost
about £20 - the customer will be happier and you won't be back
there working for free every weekend trying to get it to work.


It's one I fitted about 6 months ago. Got it from Toolstation. I
suspect it's the timer at fault because he has hot water OK in the
mornings, but not later on in the day.

I need to isolate the problem.

So shouldn't you check that the element is actually getting volts when
the timer claims to be on ?


I will indeed, but if it is getting volts it isn't necessarily heating the
water. Or is it?

Just that I don't want to change the element and not sort the problem.


--
Dave
The Medway Handyman
www.medwayhandyman.co.uk
01634 717930
07850 597257


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In message , The Medway Handyman
writes
raden wrote:
In message , The Medway
Handyman writes
Phil L wrote:
The Medway Handyman wrote:
Hi

I need to check a 3kw x 27" immersion heater element to see if it's
working. If I connect my multi meter across the terminals, what
resistance should I find?

Why bother? - sling it in the skip and fit a new one which will cost
about £20 - the customer will be happier and you won't be back
there working for free every weekend trying to get it to work.

It's one I fitted about 6 months ago. Got it from Toolstation. I
suspect it's the timer at fault because he has hot water OK in the
mornings, but not later on in the day.

I need to isolate the problem.

So shouldn't you check that the element is actually getting volts when
the timer claims to be on ?


I will indeed, but if it is getting volts it isn't necessarily heating the
water. Or is it?

Just that I don't want to change the element and not sort the problem.


If you have 240 volts across the element (at the element) then yes, it
will either heat up or it's buggered

It's either open circuit or it has a finite resistance which will
generate heat when a current is passed through it

there are no other possibilities other than in DrivelPhysics

--
geoff
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In article ,
Owain writes:
The Medway Handyman wrote:
I need to check a 3kw x 27" immersion heater element to see if it's working.
If I connect my multi meter across the terminals, what resistance should I
find?


Current will be approx 3000 / 240 = 12.9A

V / I = R therefore 240 / 12.9 = 18 ohms


Probably significantly less when cold.

--
Andrew Gabriel


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In message , raden
writes

So shouldn't you check that the element is actually getting volts when
the timer claims to be on ?


I will indeed, but if it is getting volts it isn't necessarily heating the
water. Or is it?

Just that I don't want to change the element and not sort the problem.


If you have 240 volts across the element (at the element) then yes, it
will either heat up or it's buggered

It's either open circuit or it has a finite resistance which will
generate heat when a current is passed through it

there are no other possibilities other than in DrivelPhysics


Modern thermostats are fitted with a cut out. Not likely to be Dave's
problem but seem able to add mystery to a very simple device.

regards


--
Tim Lamb
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On Sun, 21 Jan 2007 22:34:06 -0000, The Medway Handyman wrote:


It's one I fitted about 6 months ago. Got it from Toolstation. I
suspect it's the timer at fault because he has hot water OK in the
mornings, but not later on in the day.

I need to isolate the problem.


Finger trouble on part of the owner? They use all the ho****er in the
morning then don't switch it back on, or "boost" it, again for ho****er
later?

Is this an E7 instalation? If and assuming no "operator error" the boost
contacts in the timer/switch might be najjered or the boost immersion
element if it is a two element system or both. My first check would be
for mains reaching the correct element when the boost is operated.

--
Cheers
Dave. pam is missing e-mail



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gasman pete wrote:

Ohm's Law
http://www.grc.nasa.gov/WWW/K-12/Sam...w/ohmslaw.html

Nice to keep for further reference

pete


yes. But wise to realise Ohm's law is not a law, and many diy type
resistances change their R greatly depending on temp, thus making ohms
law calcs out by anything upto a factor of 10.


NT

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gasman pete wrote:

Ohm's Law
http://www.grc.nasa.gov/WWW/K-12/Sam...w/ohmslaw.html

Nice to keep for further reference

pete


yes. But wise to realise Ohm's law is not a law, and many diy type
resistances change their R greatly depending on temp, thus making ohms
law calcs out by anything upto a factor of 10. This applies
particularly to light bulbs and some heating elephants.


NT

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Tim Lamb wrote:

Modern thermostats are fitted with a cut out. Not likely to be Dave's
problem but seem able to add mystery to a very simple device.


That was exactly the problem Tim. Gold star, go to the top of the class.

Cut out had tripped. Reset the button and all is fine.

Thanks.


--
Dave
The Medway Handyman
www.medwayhandyman.co.uk
01634 717930
07850 597257




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wrote in message
s.com...
gasman pete wrote:

Ohm's Law
http://www.grc.nasa.gov/WWW/K-12/Sam...w/ohmslaw.html

Nice to keep for further reference

pete


yes. But wise to realise Ohm's law is not a law, and many diy type
resistances change their R greatly depending on temp, thus making ohms
law calcs out by anything upto a factor of 10.


Oh yes it is! The fact that R is changing doesn't affect the law, it just
affects the current to voltage relationship. For DC situations V=IR and
continues to do so as R changes.


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)


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Andrew Gabriel wrote:

V / I = R therefore 240 / 12.9 = 18 ohms


Probably significantly less when cold.


Not usually. Nichrome has a very low low temperature coefficient of
resistivity - about 60 ppm per degree, according to Kay and Laby.
That's only a 3% change in resistance over 500 deg.

--
Andy
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Bob Mannix wrote:
wrote in message
s.com...
gasman pete wrote:

Ohm's Law
http://www.grc.nasa.gov/WWW/K-12/Sam...w/ohmslaw.html

Nice to keep for further reference

pete


yes. But wise to realise Ohm's law is not a law, and many diy type
resistances change their R greatly depending on temp, thus making ohms
law calcs out by anything upto a factor of 10.


Oh yes it is! The fact that R is changing doesn't affect the law, it just
affects the current to voltage relationship. For DC situations V=IR and
continues to do so as R changes.


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

As I suspect you know, "V=IR" is not and has never been Ohm's Law
despite what nasa et al seem to think. V= IR is the definition of
resistance and that is why you are correct. Ohm's Law states that for
a metallic conductor at constant temperature, V is directly
proportional to I (ie R is constant). As I have spent all morning
trying to explain to my L6 Physics groups, nothing actually obeys the
law but many things approximate to it.

Lawrence

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In message , The Medway Handyman
writes
Tim Lamb wrote:

Modern thermostats are fitted with a cut out. Not likely to be Dave's
problem but seem able to add mystery to a very simple device.


That was exactly the problem Tim. Gold star, go to the top of the class.

Cut out had tripped. Reset the button and all is fine.


Ah!

Now for the killer question............ why did it trip?

I have just this problem with my daughter's immersion. Looks perfect.
appears to work OK but occasionally throws out the trip.

If it the thing wasn't nicely boxed in (drain cock inaccessible, don't
you just love thoughtful handymen:-) I would have thrown it away long
since.

I found the comment about missing earths a bit worrying.

regards

--
Tim Lamb
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Tim Lamb wrote:
In message , The Medway
Handyman writes
Tim Lamb wrote:

Modern thermostats are fitted with a cut out. Not likely to be
Dave's problem but seem able to add mystery to a very simple device.


That was exactly the problem Tim. Gold star, go to the top of the
class. Cut out had tripped. Reset the button and all is fine.


Ah!

Now for the killer question............ why did it trip?

I have just this problem with my daughter's immersion. Looks perfect.
appears to work OK but occasionally throws out the trip.


My local independant plumbers merchants pointed out the trip when I took the
old stat in to get a replacement. Apparently this trip thing is fairly
recent. I did ask why it tripped. Apparently they are a little sensitive
and can trip if the immersion cover has atowel over it - the temp rises and
off it goes.

I found the comment about missing earths a bit worrying.


I did check that out & all was well. Worth knowing though - good group this
innit?


--
Dave
The Medway Handyman
www.medwayhandyman.co.uk
01634 717930
07850 597257




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On Sun, 21 Jan 2007 22:34:06 +0000, The Medway Handyman wrote:

Phil L wrote:
The Medway Handyman wrote:
Hi

I need to check a 3kw x 27" immersion heater element to see if it's
working. If I connect my multi meter across the terminals, what
resistance should I find?


Why bother? - sling it in the skip and fit a new one which will cost
about £20 - the customer will be happier and you won't be back there
working for free every weekend trying to get it to work.


It's one I fitted about 6 months ago. Got it from Toolstation. I suspect
it's the timer at fault because he has hot water OK in the mornings, but not
later on in the day.


Most of the immersion heater timers I have used seem have a rather limited
life.
Probably the best and the most expensive approach is to use a proper
contactor (DIN rail and enclosure).

The Smiths electronic unit seems to be better than most of the others.



--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards
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