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Barry Young
 
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Default Immersion heater question

Hi everybody,

My flat's hot water is provided solely by a hot water cylinder with
two immersion heaters in it. Until now, only the bottom one was wired
up - the top one may have been at some point, but certainly not since
I've moved in. I'm on Economny 7, btw, and I understand the rationale
behind the two immersion heater set up.

Okay, so recently, the bottom immersion heater died on me. I think it
was probably to do with a faulty timer (which was always ON!) and
possible a suspect thermostat. I've tried putting a new thermostat in,
but no joy. I also tried removing the immersion heater to replace
after reading the many posts here on the subject. It's stuck, and I'm
scared (and there are wolves outside). Then it occurred to me, why not
just wire up the top immersion heater? So I did, and it seems to be
working fine. Now I understand that this heater is only meant as a
"top-up", but presumably if you give it long enough, the water in the
cylinder should equilibrate anyway? Because in the short-to-medium
term, I thought I might as well just use the top immersion heater,
then get a "Professional" in to replace the pair of them (or the
cylinder...) when that one goes.

What do yers reckon?
  #2   Report Post  
Set Square
 
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Default Immersion heater question

In an earlier contribution to this discussion,
Barry Young wrote:

Hi everybody,

My flat's hot water is provided solely by a hot water cylinder with
two immersion heaters in it. Until now, only the bottom one was wired
up - the top one may have been at some point, but certainly not since
I've moved in. I'm on Economny 7, btw, and I understand the rationale
behind the two immersion heater set up.

Okay, so recently, the bottom immersion heater died on me. I think it
was probably to do with a faulty timer (which was always ON!) and
possible a suspect thermostat. I've tried putting a new thermostat in,
but no joy. I also tried removing the immersion heater to replace
after reading the many posts here on the subject. It's stuck, and I'm
scared (and there are wolves outside). Then it occurred to me, why not
just wire up the top immersion heater? So I did, and it seems to be
working fine. Now I understand that this heater is only meant as a
"top-up", but presumably if you give it long enough, the water in the
cylinder should equilibrate anyway? Because in the short-to-medium
term, I thought I might as well just use the top immersion heater,
then get a "Professional" in to replace the pair of them (or the
cylinder...) when that one goes.

What do yers reckon?


The top immersion heater will only heat the top of the tank! Natural
convection ensures that there is always a temperature gradient from the top
to the bottom of the tank. If you only heat the top, the top section can be
hot enough to turn off the heater by means of its thermostat - whilst the
bottom of the tank remains quite cool.

This is fine for handwashing or the odd shower - but not a lot of use for
baths.

Is the bottom heater definitely dead? Have you measured the resistance of
the element with a stat removed? If this is open circuit then it pretty
certainly *is* dead. Otherwise, it may just be a wiring problem.

How did you try to remove it? You will, of course, have to drain the tank -
but it's easiest to *loosen* the heater whilst the tank is still full of
water - so that the weight of water stops the tank from moving while you are
applying a *lot* of torque - probably by sliding a tube over the handle of
the spanner to increase the lever arm length.
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.


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Dave Plowman (News)
 
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Default Immersion heater question

In article ,
Barry Young wrote:
Now I understand that this heater is only meant as a
"top-up", but presumably if you give it long enough, the water in the
cylinder should equilibrate anyway? Because in the short-to-medium
term, I thought I might as well just use the top immersion heater,
then get a "Professional" in to replace the pair of them (or the
cylinder...) when that one goes.


If the top mounted one has only a short element, it will only heat some of
the tank. Strange, given that water tends to circulate, but nevertheless
true.

That was the idea of the two - the lower one to heat the whole tank, the
top one just for when you only needed a small amount of hot water.

There are/were also twin length top mounting types to do the same thing.

It might be possible to remove the top one and replace it with a full
length type - they're cheap enough.

--
*A snooze button is a poor substitute for no alarm clock at all *

Dave Plowman London SW
To e-mail, change noise into sound.
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John
 
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Default Immersion heater question


"Set Square" wrote in message
...
In an earlier contribution to this discussion,
Barry Young wrote:

Hi everybody,

SNIP


Is the bottom heater definitely dead? Have you measured the resistance of
the element with a stat removed? If this is open circuit then it pretty
certainly *is* dead. Otherwise, it may just be a wiring problem.

If you are in a hard water area the element will have most likely split and
twisted out of shape. If the insulation resistance of the disconnected
heater is less than a Meg its a goner regardless of whether the element
shows open or a through circuit!

How did you try to remove it? You will, of course, have to drain the

tank -
but it's easiest to *loosen* the heater whilst the tank is still full of
water - so that the weight of water stops the tank from moving while you

are
applying a *lot* of torque - probably by sliding a tube over the handle of
the spanner to increase the lever arm length.


You have every chance of tearing a hole in the side of the cylinder if you
simply apply a high torque. Use a ring or box spanner and "tap" it round
with a hammer until the seal of jointing compound and corrosion detritus in
the threads is released. In very extreme cases application of heat may be
required as well but tapping is effective in about 95% of stuck element
cases.
Do it with the cylinder full until it just moves then drain off and continue
to undo it.


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Barry Young
 
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Default Immersion heater question

The top immersion heater will only heat the top of the tank! Natural
convection ensures that there is always a temperature gradient from the top
to the bottom of the tank. If you only heat the top, the top section can be
hot enough to turn off the heater by means of its thermostat - whilst the
bottom of the tank remains quite cool.


Yep, I was half expecting that. I've just turned up the thermostat by
a couple of notches and that seems to make it kick in again. I
understand I'm not going to have convection currents on my side this
way, but I imagine conduction through the water and the tank body
itself will help to at least partially address this.

This is fine for handwashing or the odd shower - but not a lot of use for
baths.


Well I've successfully run one bath from my new set-up! I'll have to
try again tomorrow in the evening after the hot water's been sitting
around all day.

Is the bottom heater definitely dead? Have you measured the resistance of
the element with a stat removed? If this is open circuit then it pretty
certainly *is* dead. Otherwise, it may just be a wiring problem.


I haven't measured the resistance, but certainly when you switch it
on, there's very little response from the little turny wheel in the
electricity meter. I used the same wiring on the top immersion heater
and it works fine, so I'm pretty sure the actual heater's kaput.

How did you try to remove it? You will, of course, have to drain the tank -
but it's easiest to *loosen* the heater whilst the tank is still full of
water - so that the weight of water stops the tank from moving while you are
applying a *lot* of torque - probably by sliding a tube over the handle of
the spanner to increase the lever arm length.


I got one of those box spanners and applied a hairdryer for a while.
Nothing happening apart from some a few groaning noises. I'll drown it
in WD40 and see if it's any more cooperative tomorrow.


  #6   Report Post  
Barry Young
 
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Default Immersion heater question

It might be possible to remove the top one and replace it with a full
length type - they're cheap enough.


There's a thought. I hadn't actually bothered trying to unscrew this
one as it wasn't broken.

I'm going to try my current set up for a week or two with different
thermostat settings and with the timer on for different lenghts of
time.
  #7   Report Post  
Dave Plowman (News)
 
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Default Immersion heater question

In article ,
Barry Young wrote:
This is fine for handwashing or the odd shower - but not a lot of use
for baths.


Well I've successfully run one bath from my new set-up! I'll have to try
again tomorrow in the evening after the hot water's been sitting around
all day.


I'd say if you've got a decent bath out of it, it's a full length type.
The short ones normally fitted only give a few basins full.

--
*A nest isn't empty until all their stuff is out of the attic

Dave Plowman London SW
To e-mail, change noise into sound.
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Dave Plowman (News)
 
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Default Immersion heater question

In article ,
Will wrote:
It might be possible to remove the top one and replace it with a full
length type - they're cheap enough.


The only problem here is that where two immersion bosses are
fitted, they are - ime - always mounted in the side of the tank. So
even if the tank were large enough to fit a longer element into in the
horizontal plane, it would make no difference to the volume of water
heated...


Right. I assumed the top one was in the 'conventional' position.

--
*Funny, I don't remember being absent minded.

Dave Plowman London SW
To e-mail, change noise into sound.
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Will
 
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Default Immersion heater question

On Fri, 09 Jul 2004 11:14:29 +0100, "Dave Plowman (News)"
wrote:



If the top mounted one has only a short element, it will only heat some of
the tank. Strange, given that water tends to circulate, but nevertheless
true.

That was the idea of the two - the lower one to heat the whole tank, the
top one just for when you only needed a small amount of hot water.

There are/were also twin length top mounting types to do the same thing.

It might be possible to remove the top one and replace it with a full
length type - they're cheap enough.


The only problem here is that where two immersion bosses are
fitted, they are - ime - always mounted in the side of the tank. So
even if the tank were large enough to fit a longer element into in the
horizontal plane, it would make no difference to the volume of water
heated...

--
Regards,

Will.
  #10   Report Post  
Christian McArdle
 
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Default Immersion heater question

I haven't measured the resistance, but certainly when you switch it
on, there's very little response from the little turny wheel in the
electricity meter. I used the same wiring on the top immersion heater
and it works fine, so I'm pretty sure the actual heater's kaput.


That isn't enough to be sure. Frequently it is the heater's internal
thermostat that blows. These can usually be replaced without removing the
immersion. It is worth checking to see, even if it does turn out to be the
element anyway. The thermostat is usually a long thin rod that slides into a
tube visible when you remove the cover cap.

Christian.





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Set Square
 
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Default Immersion heater question

In an earlier contribution to this discussion,
Christian McArdle wrote:

I haven't measured the resistance, but certainly when you switch it
on, there's very little response from the little turny wheel in the
electricity meter. I used the same wiring on the top immersion heater
and it works fine, so I'm pretty sure the actual heater's kaput.


That isn't enough to be sure. Frequently it is the heater's internal
thermostat that blows. These can usually be replaced without removing
the immersion. It is worth checking to see, even if it does turn out
to be the element anyway. The thermostat is usually a long thin rod
that slides into a tube visible when you remove the cover cap.

Christian.


.. . . and wired in series with the element. That was why I suggested
removing the stat and measuring the resistance of the *element* - thus
eliminating any problems with the stat or connections.

--
Cheers,
Set Square
______
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Christian McArdle
 
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Default Immersion heater question

. . . and wired in series with the element. That was why I suggested
removing the stat and measuring the resistance of the *element* - thus
eliminating any problems with the stat or connections.


Indeed. The OP, though, had only seen that it wasn't drawing current at the
meter and hadn't done what you suggested.

Christian.


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