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UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions. |
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#1
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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 |
#2
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Immersion Heater
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 |
#3
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Immersion Heater
"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 |
#4
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Immersion Heater
"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 |
#5
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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 |
#6
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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. |
#7
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Immersion Heater
"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 |
#8
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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? 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 |
#9
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Immersion Heater
Ohm's Law
http://www.grc.nasa.gov/WWW/K-12/Sam...w/ohmslaw.html Nice to keep for further reference pete |
#10
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Immersion Heater
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 |
#11
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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. |
#12
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Immersion Heater
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 |
#13
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Immersion Heater
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 |
#14
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Immersion Heater
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 |
#15
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Immersion Heater
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 |
#16
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Immersion Heater
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 |
#17
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Immersion Heater
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 |
#18
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Immersion Heater
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 |
#19
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Immersion Heater
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 |
#20
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Immersion Heater
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 |
#21
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Immersion Heater
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) |
#22
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Immersion Heater
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 |
#23
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Immersion Heater
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 |
#24
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Immersion Heater
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 |
#25
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Immersion Heater
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 |
#26
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Immersion Heater
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#27
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Immersion Heater
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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