Hello,

I know new immersion heaters have a second thermal cut out so that if
the thermostat fails, the water does not boil but how recently was
this introduced?

For old immersion heaters, if the stat fails what happens? Does if
fail on, fail off, or is it fifty-fifty what happens?

I think my stat has broken. We heat our water overnight on economy
seven and this morning the water is scalding hot.

Our cylinder has two horizontally mounted immersion heaters: one at
the bottom and one two-thirds of the way up. Both immersion heaters
have the same writing on their covers, so I think they are identical.

I have isolated the electricity and removed the covers. If I turn the
dial on the thermostat of the top heater, I can hear it click on and
off as I vary the setting.

If I change the setting on the bottom thermostat it never clicks. Is
the absence of the click proof it is broken?

I didn't think to measure the resistance of the stat whilst it was hot
and in the cylinder and at the moment it out of the cylinder and cold.
I will put it back into the cylinder and then measure the resistance.

I know I can buy replacement stats but I am unsure which I need. The
writing on the immersion heater says it is a 14 inch heater. Looking
on plumbers' merchants' web sites it appears that 14 inch heaters have
seven inch thermostats but this one measures 11 or 12 inches (do you
measure the rod or the whole length?). So should I buy an 11 inch one?

The heater says "Backer maxistore anti corrosive, type 314c 825,
355mm, 14 inch, 3kW"

How long do the stats normally last. Is it worth buying a spare or
shall I wait for one to blow first?

Whilst browsing these web sites I see some heaters are for
"aggressive" water. Does that just mean hard water? At what point is
water classed as "aggressive"? This is just me wondering, I'm hoping
just to change the stat as the heater obviously works and draining the
cylinder to change a heater sounds daunting. I've also heard cylinders
can be damaged if you cross thread the heater.

I hadn't paid too much attention to immersion heaters until today. I
hadn't realised they are all 3 kW; I thought the larger ones were
higher rated. I realise that the 3kW limit is probably due to cable
ratings but if we can run bigger cables to cookers and electric
showers, why isn't it common practice to use bigger cables to
immersion heaters and use more powerful heaters? This would allow the
cylinder to heat up faster.

I had not realised that the top heater is only used for boost and the
bottom heater only used for overnight. I always thought they came on
together. I realise this is due to the cable again but it does seem
silly having a top heater that is never used.

The heaters are controlled by something like this:
http://www.screwfix.com/prods/44419/...rtz-Timeswitch

It must have a battery inside because it ticks away even when he power
is switched off. I always thought this seemed over the top but I
realise now that it must have to switch between the two heaters. I
presume it would not let you use boost heater at the same time as the
economy seven one.

Is there a reason that butyl cables are used with immersion heaters? I
know they have to be heat resistant but why not heat resistant PVC? I
always find PVC easier to cut.

Thanks,
Stephen.

"Stephen" wrote in message
...
Hello,

I know new immersion heaters have a second thermal cut out so that if
the thermostat fails, the water does not boil but how recently was
this introduced?

For old immersion heaters, if the stat fails what happens? Does if
fail on, fail off, or is it fifty-fifty what happens?

I think my stat has broken. We heat our water overnight on economy
seven and this morning the water is scalding hot.

Our cylinder has two horizontally mounted immersion heaters: one at
the bottom and one two-thirds of the way up. Both immersion heaters
have the same writing on their covers, so I think they are identical.

I have isolated the electricity and removed the covers. If I turn the
dial on the thermostat of the top heater, I can hear it click on and
off as I vary the setting.

If I change the setting on the bottom thermostat it never clicks. Is
the absence of the click proof it is broken?

I didn't think to measure the resistance of the stat whilst it was hot
and in the cylinder and at the moment it out of the cylinder and cold.
I will put it back into the cylinder and then measure the resistance.

I know I can buy replacement stats but I am unsure which I need. The
writing on the immersion heater says it is a 14 inch heater. Looking
on plumbers' merchants' web sites it appears that 14 inch heaters have
seven inch thermostats but this one measures 11 or 12 inches (do you
measure the rod or the whole length?). So should I buy an 11 inch one?

The heater says "Backer maxistore anti corrosive, type 314c 825,
355mm, 14 inch, 3kW"

How long do the stats normally last. Is it worth buying a spare or
shall I wait for one to blow first?

Whilst browsing these web sites I see some heaters are for
"aggressive" water. Does that just mean hard water? At what point is
water classed as "aggressive"? This is just me wondering, I'm hoping
just to change the stat as the heater obviously works and draining the
cylinder to change a heater sounds daunting. I've also heard cylinders
can be damaged if you cross thread the heater.

I hadn't paid too much attention to immersion heaters until today. I
hadn't realised they are all 3 kW; I thought the larger ones were
higher rated. I realise that the 3kW limit is probably due to cable
ratings but if we can run bigger cables to cookers and electric
showers, why isn't it common practice to use bigger cables to
immersion heaters and use more powerful heaters? This would allow the
cylinder to heat up faster.

I had not realised that the top heater is only used for boost and the
bottom heater only used for overnight. I always thought they came on
together. I realise this is due to the cable again but it does seem
silly having a top heater that is never used.

The heaters are controlled by something like this:
http://www.screwfix.com/prods/44419/...rtz-Timeswitch

It must have a battery inside because it ticks away even when he power
is switched off. I always thought this seemed over the top but I
realise now that it must have to switch between the two heaters. I
presume it would not let you use boost heater at the same time as the
economy seven one.

Is there a reason that butyl cables are used with immersion heaters? I
know they have to be heat resistant but why not heat resistant PVC? I
always find PVC easier to cut.

Thanks,
Stephen.

Sounds like the contacts have welded themselves together.

If you don't use a lot of water then the top one can be used on its own to
just heat some of the water.

As the heaters are horizontal the length of the thermostat isn't important
to the way it operates.

I am sure more specific responses will soon follow.

"Stephen" wrote in message
...

I had not realised that the top heater is only used for boost and the
bottom heater only used for overnight. I always thought they came on
together. I realise this is due to the cable again but it does seem
silly having a top heater that is never used.

The top heater is very good if you want a limited supply of hot water as it
doesn't heat the entire tank.
An example would be for a shower rather than a bath.


The heaters are controlled by something like this:
http://www.screwfix.com/prods/44419/...rtz-Timeswitch

The longer/bottom heater will be used at night on economy 7 (if it still
exists) to heat the whole tank.
If you run low you use the top one to heat a bit at the top on full rate
electricity.

If you don't have economy rate electricity use the top one only for anything
that doesn't require lots of hot water, or get a gas heater.

On Aug 20, 9:07*am, Stephen wrote:
Hello,

I know new immersion heaters have a second thermal cut out so that if
the thermostat fails, the water does not boil but how recently was
this introduced?

For old immersion heaters, if the stat fails what happens? Does if
fail on, fail off, or is it fifty-fifty what happens?
I think my stat has broken. We heat our water overnight on economy
seven and this morning the water is scalding hot.

sounds like it.

Our cylinder has two horizontally mounted immersion heaters: one at
the bottom and one two-thirds of the way up. Both immersion heaters
have the same writing on their covers, so I think they are identical.

I have isolated the electricity and removed the covers. If I turn the
dial on the thermostat of the top heater, I can hear it click on and
off as I vary the setting.

If I change the setting on the bottom thermostat it never clicks. Is
the absence of the click proof it is broken?

depends on the water temp. If the water's ice cold, no, if its
scalding no, if its somewhere between the 2, yes.


I didn't think to measure the resistance of the stat whilst it was hot
and in the cylinder and at the moment it out of the cylinder and cold.
I will put it back into the cylinder and then measure the resistance.

you already know it failed

I know I can buy replacement stats but I am unsure which I need. The
writing on the immersion heater says it is a 14 inch heater. Looking
on plumbers' merchants' web sites it appears that 14 inch heaters have
seven inch thermostats but this one measures 11 or 12 inches (do you
measure the rod or the whole length?). So should I buy an 11 inch one?

The heater says "Backer maxistore anti corrosive, type 314c 825,
355mm, 14 inch, 3kW"

How long do the stats normally last. Is it worth buying a spare or

no

shall I wait for one to blow first?

Whilst browsing these web sites I see some heaters are for
"aggressive" water. Does that just mean hard water? At what point is
water classed as "aggressive"? This is just me wondering, I'm hoping
just to change the stat as the heater obviously works and draining the
cylinder to change a heater sounds daunting.

When replacing a heater you should have the tank full initially, once
its loose then turn tap on and water supply of to drain it.

I've also heard cylinders
can be damaged if you cross thread the heater.

I hadn't paid too much attention to immersion heaters until today. I
hadn't realised they are all 3 kW;

they arent

I thought the larger ones were
higher rated. I realise that the 3kW limit is probably due to cable
ratings but if we can run bigger cables to cookers and electric
showers, why isn't it common practice to use bigger cables to
immersion heaters and use more powerful heaters? This would allow the
cylinder to heat up faster.

a) no need
b) more cost

I had not realised that the top heater is only used for boost and the
bottom heater only used for overnight. I always thought they came on
together. I realise this is due to the cable again but it does seem
silly having a top heater that is never used.

nothing to do with cable. The top one heats a smaller volume of water,
so it gives you hot water quicker. Bottom one is run on E7, top one is
used during the day if needed for a topup.

The heaters are controlled by something like this:http://www.screwfix.com/prods/44419/...ating-Controls...

It must have a battery inside because it ticks away even when he power
is switched off. I always thought this seemed over the top but I
realise now that it must have to switch between the two heaters. I
presume it would not let you use boost heater at the same time as the
economy seven one.

Is there a reason that butyl cables are used with immersion heaters? I
know they have to be heat resistant but why not heat resistant PVC? I

no such thing

always find PVC easier to cut.

Thanks,
Stephen.

NT

On Thu, 20 Aug 2009 04:18:22 -0700 (PDT), NT
wrote:

When replacing a heater you should have the tank full initially, once
its loose then turn tap on and water supply of to drain it.

But don't they drain from the top? I thought cold water went in the
bottom and hot water came out the top?

Is there a reason that butyl cables are used with immersion heaters? I
know they have to be heat resistant but why not heat resistant PVC? I

no such thing

There's both he
http://www.tlc-direct.co.uk/Main_Ind...ant/index.html

Stephen wrote:
On Thu, 20 Aug 2009 04:18:22 -0700 (PDT), NT
wrote:

When replacing a heater you should have the tank full initially, once
its loose then turn tap on and water supply of to drain it.

But don't they drain from the top? I thought cold water went in the
bottom and hot water came out the top?

Is there a reason that butyl cables are used with immersion heaters? I
know they have to be heat resistant but why not heat resistant PVC? I
no such thing

There's both he
http://www.tlc-direct.co.uk/Main_Ind...ant/index.html
Turning on a hot tap will not drain the tank. Turn on or opening the
drain cock will.
There is no need to remove the element to change the thermostat.
If you are not using the top heater then why not swap the stats over for
now and get a replacement at your leisure. £6-7 from toolstation and you
are bound to find something else they sell to get to the £10 post free
threshold. Maybe even buy 2 to get the protection of the new type on
both your heaters?

Bob

On Thu, 20 Aug 2009 16:50:22 +0100, Bob Minchin
wrote:

Turning on a hot tap will not drain the tank. Turn on or opening the
drain cock will.

That's what I thought. Our posts must have crossed. I presume the
drain cock is on the cold fill pipe? I'm not sure that mine has one.
Even if it does, the pipe goes behind the cylinder, so I can't get to
it without demolishing a wall ;(

There is no need to remove the element to change the thermostat.

I know. It was just the whole episode got me into thinking about
immersion heaters so after my initial questions about thermostats, I
started musing about everything else!

If you are not using the top heater then why not swap the stats over for
now and get a replacement at your leisure.

Good idea but I've already ordered two.

Maybe even buy 2 to get the protection of the new type on
both your heaters?

Great minds think a like and all that. I don't use the boost function
there's always plenty of hot water left at the end of each day from
the overnight warm, but even so, I thought for the cost of a couple of
pounds, I would replace both so that both have the new safety cut out.

Thanks again.
Stephen.

On Thu, 20 Aug 2009 09:48:09 +0100, "John"
wrote:

As the heaters are horizontal the length of the thermostat isn't important
to the way it operates.

Why are they so short relative to the length of the heater? Is it so
they measure the temperature of the hotter water nearer the top of the
heater, rather than the colder water below?

On Thu, 20 Aug 2009 09:51:43 +0100, "dennis@home"
wrote:

The longer/bottom heater will be used at night on economy 7 (if it still
exists) to heat the whole tank.
If you run low you use the top one to heat a bit at the top on full rate
electricity.

We always have plenty of HW left at the end of the day. Perhaps I
should use the top one on economy seven to just warm half a tank?!

"Stephen" wrote in message
...
On Thu, 20 Aug 2009 09:51:43 +0100, "dennis@home"
wrote:

The longer/bottom heater will be used at night on economy 7 (if it still
exists) to heat the whole tank.
If you run low you use the top one to heat a bit at the top on full rate
electricity.

We always have plenty of HW left at the end of the day. Perhaps I
should use the top one on economy seven to just warm half a tank?!

If there is enough it will save you money.
You can swap the wires and try it out.

On Aug 20, 3:16*pm, Stephen wrote:
On Thu, 20 Aug 2009 04:18:22 -0700 (PDT), NT
wrote:

When replacing a heater you should have the tank full initially, once
its loose then turn tap on and water supply of to drain it.

But don't they drain from the top? I thought cold water went in the
bottom and hot water came out the top?

Is there a reason that butyl cables are used with immersion heaters? I
know they have to be heat resistant but why not heat resistant PVC? I

no such thing

There's both hehttp://www.tlc-direct.co.uk/Main_Ind..._Heat_Resistan...

Well... I sense confusion. Yes there's 90C pvc versus 70, the term
'heat resistant' only means its to some degree more heat resistant
than the more common pvc, that doesnt make it comparable to high temp
cables such as butyl rubber.

Then there's also the q of what happens when temp rating is exceeded,
rubber and pvc behave somewhat differently.


NT

On Aug 20, 9:45*pm, NT wrote:
On Aug 20, 3:16*pm, Stephen wrote:

On Thu, 20 Aug 2009 04:18:22 -0700 (PDT), NT
wrote:

When replacing a heater you should have the tank full initially, once
its loose then turn tap on and water supply of to drain it.

But don't they drain from the top? I thought cold water went in the
bottom and hot water came out the top?

Is there a reason that butyl cables are used with immersion heaters? I
know they have to be heat resistant but why not heat resistant PVC? I

no such thing

There's both hehttp://www.tlc-direct.co.uk/Main_Ind..._Heat_Resistan...

Well... I sense confusion. Yes there's 90C pvc versus 70, the term
'heat resistant' only means its to some degree more heat resistant
than the more common pvc, that doesnt make it comparable to high temp
cables such as butyl rubber.

Then there's also the q of what happens when temp rating is exceeded,
rubber and pvc behave somewhat differently.

NT



There's to some extent differing meanings to 'high temp' in this
situation. PVC flex can be rated to 90C, but running 13A through it
_and_ connecting it to 70C heater connections will likely overheat it.
The butyl rubber leads used on immersions have much thicker conductors
to minimise self heating, and enable them to function ok when
connected to a hot heater.


NT

On Thu, 20 Aug 2009 13:45:01 -0700 (PDT), NT
wrote:

Well... I sense confusion. Yes there's 90C pvc versus 70, the term
'heat resistant' only means its to some degree more heat resistant
than the more common pvc, that doesnt make it comparable to high temp
cables such as butyl rubber.

Then there's also the q of what happens when temp rating is exceeded,
rubber and pvc behave somewhat differently.

I'm happy to admit I may be confused because I am certainly not an
expert but shouldn't TLC know better? Why are they advertising it as
immersion cable if it would be dangerous to do so?

What happens to butyl and PVC cables when they overheat?

Hello again,

Just to say that I have received two thermostats from BES. I believe
they are made by Banico. If I have a slight grumble it is that only
60C is marked on and the other temperatures are "max" and "min",
whatever they are. Also these are marked white on white, so they are
difficult to see. OTOH I suppose you only have to set it once.

When I changed the bottom thermostat there was some fine white powder
inside the immersion heater. Whatever could that have been? There was
no powder in the otherwise identical top heater.

The head of the slotted nut that retains the cover on the one heater
is a bit chewed up, making it difficult to grip with a screwdriver.
Any suggestions on how to grind a new slot into it?

The new thermostats have a small metal disc on the rear, which I
presume is the safety thermal cut out. Should this be touching the
cylinder, because I'm afraid they don't in my heaters?

Thanks again,
Stephen.

On Aug 21, 3:12*pm, Stephen wrote:
On Thu, 20 Aug 2009 13:45:01 -0700 (PDT), NT
wrote:

Well... I sense confusion. Yes there's 90C pvc versus 70, the term
'heat resistant' only means its to some degree more heat resistant
than the more common pvc, that doesnt make it comparable to high temp
cables such as butyl rubber.

Then there's also the q of what happens when temp rating is exceeded,
rubber and pvc behave somewhat differently.

I'm happy to admit I may be confused because I am certainly not an
expert but shouldn't TLC know better? Why are they advertising it as
immersion cable if it would be dangerous to do so?

What makes you think their immersion heater cable may be dangerous?


What happens to butyl and PVC cables when they overheat?

Short term pvc goes very soft, conductors migrate through it, and
fires tend to happen. Long term is hardens and falls apart
Rubber suffers no ill effect short term, long term it hardens and
breaks.


NT

On Fri, 21 Aug 2009 13:42:40 -0700 (PDT), NT
wrote:

What makes you think their immersion heater cable may be dangerous?

Sorry, I thought you said in your earlier answer that even a 90 degree
rated PVC cable might overheat when connected to an immersion heater,
implying that PVC should not be used for this purpose?

What happens to butyl and PVC cables when they overheat?

Short term pvc goes very soft, conductors migrate through it, and
fires tend to happen. Long term is hardens and falls apart
Rubber suffers no ill effect short term, long term it hardens and
breaks.

So rubber has benefits in the short term but long term prospects are
bad with either?

BTW, how accurate are the thermostats? If set to 60C will I get 60C,
or 55-65C, or 50-70C, etc? I know I am supposed to set it to 60C to
kill all the bugs, will that be high enough?

Thanks again.

We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember Stephen
saying something like:

I had not realised that the top heater is only used for boost and the
bottom heater only used for overnight. I always thought they came on
together. I realise this is due to the cable again but it does seem
silly having a top heater that is never used.

Clue - Bath and Sink.

On Aug 22, 2:17*pm, Stephen wrote:
On Fri, 21 Aug 2009 13:42:40 -0700 (PDT), NT
wrote:

What makes you think their immersion heater cable may be dangerous?

Sorry, I thought you said in your earlier answer that even a 90 degree
rated PVC cable might overheat when connected to an immersion heater,
implying that PVC should not be used for this purpose?

If youre saying they're selling pvc flex as good for immersion heaters
it would be interesting to see.


What happens to butyl and PVC cables when they overheat?

Short term pvc goes very soft, conductors migrate through it, and
fires tend to happen. Long term is hardens and falls apart
Rubber suffers no ill effect short term, long term it hardens and
breaks.

So rubber has benefits in the short term but long term prospects are
bad with either?

Of course overloaded or overheated cable has poor prospects, thats
what overheated and overloaded mean.


BTW, how accurate are the thermostats? If set to 60C will I get 60C,
or 55-65C, or 50-70C, etc?

Last time I looked at specs for one it had huge hysteresis.


NT

On Sat, 22 Aug 2009 10:53:45 -0700 (PDT), NT
wrote:

If youre saying they're selling pvc flex as good for immersion heaters
it would be interesting to see.

This is what they say: "General Purpose - Pvc Heat Resistant Cables
Application: Immersion heaters, Storage Heaters, Radiant fires and
longer runs of low voltage lighting. Other applications that require
flexible heat resistant cable Not be used in areas where the cable may
come into contact with grease or oil. Current Rating: 16 Amps"

Short term pvc goes very soft, conductors migrate through it, and
fires tend to happen. Long term is hardens and falls apart
Rubber suffers no ill effect short term, long term it hardens and
breaks.

So rubber has benefits in the short term but long term prospects are
bad with either?

Of course overloaded or overheated cable has poor prospects, thats
what overheated and overloaded mean.


Sorry, I knew that, what I meant to say was the rubber has the
advantage of being safer in short term situations but you are quite
right, it shouldn't be overloaded in the first place.

BTW, how accurate are the thermostats? If set to 60C will I get 60C,
or 55-65C, or 50-70C, etc?

Last time I looked at specs for one it had huge hysteresis.

I'm best to set it to 70C then just to be sure.