Immersion heater failure

[voicey]

Hi guys - it's been a while since I've posted on here (my flat renovation got finished nicely partly thanks to the info on this forum).

I have read through previous postings but I would like someone to check my logic before I embark on a repair.

I returned home last night to find no hot water in the tank (we have Economy 7 with a boost at lunchtime). The tank has two elements - the bottom connected to the E7 and one half way up connected to the permanent supply (switched on the wall).

First of all I checked the fuse to the immersion heater (we have old style fuses - checked with continuity tester and it was good). So I waited until 10pm when the first evening period of cheap electricity starts in order to conduct some further testing (with multimeter). There was 250v at the feed to the thermostat. There was also 250v on the other side of the thermostat. The lead coming off the other side of the thermostat went into something else before it reached the element. However, there was 250v at the element. I looked for a reset button but there was none.

Next I disconnected the supply (fuse and switch) so I could measure the resistance across the element. I also measured the resistance of the working element further up the tank. The bottom element measured 15,000 ohms whilst the top was 23ohms. Does the fact that the wires were still connected matter? I have concluded that the element itself has gone and needs to be replaced. Is there anything else I should test before embarking on the repair?

Also - I have seen on the screwfix website there are two sizes of element - 11" and 27". Is it just a matter of what will fit into my tank or are there other considerations to make when choosing?

I'm OK for hot water at the moment - I switched the E7 supply with the permanent so the E7 now powers the top heater.

Apologies for the questions and thanks in advance.

Voicey.

 

[ChrisR]

Next I disconnected the supply (fuse and switch) so I could measure the resistance across the element. I also measured the resistance of the working element further up the tank. The bottom element measured 15,000 ohms whilst the top was 23ohms. Does the fact that the wires were still connected matter?
Not if it's all really "Off"
I have concluded that the element itself has gone and needs to be replaced. Is there anything else I should test before embarking on the repair?
No, looks like your logic's correct to me!

Also - I have seen on the screwfix website there are two sizes of element - 11" and 27". Is it just a matter of what will fit into my tank
Yes, you usually have to use shorties if they're sideways

or are there other considerations to make when choosing?

Not really. The Extra thing you found was probably a safety stat set to 95 or so. They're integral with the thermostats now

Apologies for the questions and thanks in advance.
Don't aplologise, it's what we do, for some reason!

 

[voicey]

Thank you for the very quick reply. My elements are horizontal so it looks like I'll be buying the 11" or shorties as you call them (mind you some people would consider 11" to be quite long ).

One more question I have thought of - should I use PTFE tape on the threads of the new element?

Cheers...

 

[voicey]

I replaced the heater today. Not a bad job, just a little time consuming emptying the tank into a bowl.

I have had both the heater running for about 1.5 hours now (we get a 2hr boost of E7 at lunchtime). The top heater is red hot but the lower one is not. There is 250v on both sides of the thermostat and across the element The element also has a resistance of 20ohms - so far so good.

Is there a reason why for the difference in temps between the two elements? Are newer ones better insulated or is it that my element is busted? I'm getting a little worried....

 

[seco services]

remember heat rises.

 

[JohnD]

the heat from the lower element rises upwards due to convection. All the hot water collects at the top of the cylinder. As the amount of hot water increases it slowly reaches down towards the bottom of the cylinder.

The upper element heats a few gallons at the top of the cylinder quite quickly.

the lower heater will take a long time to heat the entire cylinder. this is correct.

I hope you have a good thick insulating jacket or two round the cylinder otherwise you are wasting money using it as a big radiator

 

[voicey]

OK - thanks guys. The tank is encased in thick green foam insulation. It isn't warm to touch so I figured it was doing it job ok and there's no need for an additional jacket - correct me if I'm worng though!

 

[JohnD]

the foam is fine (I have a jacket over mine as well as I had a near-new one from the cylinder it replaced). You can get rigid foam lagging sleeves for the hot pipes which also help.

 

[kirkgas]

i am a plumber to trade so sparkies will be horrified at my non technical test to see if an immersor is working but hey ho, because they use up so much leccy the best way to see if an immersor is working is to get someone to switch it on and off while you look at the dial on the leccy meter when the immersor is off the dial spins slowly due to lights and sockets being on, as soon as you flick the immersor switch the dial goes mental as i said it isn't to technical but if you are not a spark you don't get involved with testing something potentially dangerous
come on sparkies shoot me down!!!!!!!!!!!!!

 

[Bamber gaspipe]

Don't aplologise, it's what we do, for some reason!

Gordon Bennett, the tears are literally streamin` from me eyes Guv`nor, is it Christmas??

 

[Meldrew's mate]

...the best way to see if an immersor is working is to get someone to switch it on and off while you look at the dial on the leccy meter when the immersor is off the dial spins slowly due to lights and sockets being on, as soon as you flick the immersor switch the dial goes mental!...

Not a bad gauge if there's a whizzy (non-technical) meter rather than a digital one, and the washing machine, microwave, dryer or kettle aren't on.....

....but that leads to the question what do you do if it's failed; and more to the point, why ask you to check it if you can't legally change it?

 

[Bamber gaspipe]

...the best way to see if an immersor is working is to get someone to switch it on and off while you look at the dial on the leccy meter when the immersor is off the dial spins slowly due to lights and sockets being on, as soon as you flick the immersor switch the dial goes mental!...

Not a bad gauge if there's a whizzy (non-technical) meter rather than a digital one, and the washing machine, microwave, dryer or kettle aren't on.....

....but that leads to the question what do you do if it's failed; and more to the point, why ask you to check it if you can't legally change it?

Load of b*ollox, use neon screwdriver or a multimeter .

 

[Rob]

Load of b*ollox, use neon screwdriver or a multimeter .

Like to see your screwdriver prove the element has a 15kohm resistance.

But hey, aslong as the thermostat is making that little light come one all is correct, right?

 

[WDIK]

ive found this neutral, does anyone know who it belongs to?

ps an accurate and safe method of testing, is to use a device such as a fluke 600
not only will it not explode in your hands or kill you
(multimeters not recommended or approved)
when testing live 240vac
(its got fused leads)
and it has an open jawed ammeter to test the load

 

[voicey]

Well the best part of three years have passed since I did this job and today we woke to cold water. The good news is that it's just the reset swtich on the thermostat that popped out and we now have hot water.

Is this the start of something going wrong? The element has been faultless and used pretty much every night since being replaced. I put an incaloy element in - should I replace it? I'm tempted to replace the thermostat in any case.