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Immersion thermo keeps tripping out!!

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mikell

from United Kingdom

Joined: 18 Sep 2006
Posts: 154
Location: Liverpool,
United Kingdom

PostPosted: Sat Jun 06, 2009 11:44 pm Reply with quote

I have an old primatic emmersion heater ,less said about that the better!
but anyway my thermostat kept tripping out so I kept resetting it and the element would work for a time but then the thermo would trip out again.
I bought a new thermostat but have the same problem,do you think the element is on the way out,I hope its not that as The tank is buckled from the last time ( 500 year old primatic ,see earlier posts!!) so dont think it would handle another removal and they are so hard to come by ( I have been told!
Any thoughts please gents and thanks for reading once more!
cheers!
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JohnD

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PostPosted: Sat Jun 06, 2009 11:55 pm Reply with quote

how hot is the water when it trips?

is it heated by boiler? Is there a cyl stat and a means to prevent the boiler overheating the cylinder?

do you mean the Overheat safety cutout in the immersion heater?

show us a pic of the connections under the cap. It should not keep overheating. Perhaps it is wired wrong

Consider converting to a normal indirect cylinder and dumping the primatic
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Agile

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PostPosted: Sun Jun 07, 2009 12:18 am Reply with quote

He means the electric immersion heater element.

They are not designed to heat the water up to near boiling point.

Reduce the temperature setting to aboiut 55C and check the wire connecter terminal screws are tight.

Tony
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gaspro1981

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PostPosted: Sun Jun 07, 2009 8:13 am Reply with quote

you need to replace the immersion thermostat icon_rolleyes.gif
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JohnD

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PostPosted: Sun Jun 07, 2009 8:54 am Reply with quote

mikell wrote:
...I bought a new thermostat but have the same problem,...


JohnD wrote:
how hot is the water when it trips?
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gaspro1981

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PostPosted: Sun Jun 07, 2009 8:58 am Reply with quote

it can only be the thermostat icon_rolleyes.gif
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JohnD

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PostPosted: Sun Jun 07, 2009 9:21 am Reply with quote

might well be

unless, for example, it has a Gravity feed from the boiler, with no zone valve, so it just gets hotter and hotter whenever the boiler is on?

Or, for example, he had wired the new immersion heater incorrectly and bypassed the thermostat?
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picasso

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PostPosted: Sun Jun 07, 2009 9:52 am Reply with quote

is there a shower pump connected to your primatic cylinder? I have come across this when the shower pump is running the top of the cylinder runs dry and trips the stat. (because the cold feed is blocked or under sized) its not a good idea to have pump with primatics as they can interfere with the internal bubble.
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mikell

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Joined: 18 Sep 2006
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Location: Liverpool,
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PostPosted: Sun Jun 07, 2009 11:50 am Reply with quote

thanks for all the info guys.
I didnt mention , the first thermostat after resetting the trip out switch a number of times, has burned out where the live wire conected.
This morning the new one has gone the same way ,plastic is slightly charred and bulbous where the live wire conected.
could this be down to myself not conecting the wire correctly ( although I did put it in and screw it tight,the wire is also as old as the boiler it is sheathed in a woven sleeve,not rubber).
I can use the boiler to heat up the rads and emmersion but only use this element for hot water only ,it has no shower pump ,its just used for heating water for baths .
Im sure it tripped at a lower temp,first but I did turn it up to about 75o .

The more i think about it Im drawn to the live wire conection,it is a bit tatty where i pushed it in ,could the faults I have be because of this ,I could crop it all and try it again when I buy another thermostat,do you think?

will try to take a photo but dont hold your breath,im no david bailey!!
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Agile

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PostPosted: Sun Jun 07, 2009 12:00 pm Reply with quote

Agile wrote:
He means the electric immersion heater element.

They are not designed to heat the water up to near boiling point.

Reduce the temperature setting to about 55C and check the wire connecter terminal screws are tight.

Tony


Thats why I asked you to check that the screws are tight !

Also its kind of illegal to run the hot water above 60C !

If the wire is in poor condition this will cause arcing as you have seen.

Surely you can strip it back to a wire in good condition or replace with 2.5 mm heat resisting cable back to the fused spur? Cable at Screwfix.

Tony
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mikell

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Joined: 18 Sep 2006
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Location: Liverpool,
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PostPosted: Sun Jun 07, 2009 12:06 pm Reply with quote

Thanks tony.
I will do as you say, but it was tight ,just a little bit frayed! icon_redface.gif
only very little though ,but hope it was this!
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mikell

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Joined: 18 Sep 2006
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Location: Liverpool,
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PostPosted: Sun Jun 07, 2009 1:57 pm Reply with quote

I have just cut it down to a neat end reconected to thermo and its working ,even though plastic is black where like you said tony it arced.
it is working for now but i will keep an eye on it.
also on the therostat the little black arrow that heads between 30o and 75o, while I was clearing it it has gone around from it original position,is there a way of knowing that it is correct ( still btween 30-75 and not now btween say,150o-200o ,id imagine it would trip first again before overheating?
or is it set to a max however many times it turns round?
thanks guys.
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JohnD

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PostPosted: Sun Jun 07, 2009 2:05 pm Reply with quote

once copper has got hot, it becomes soft and will not make a reliable connection, but will become loose and burn again. This applies to the wire and the terminal in the thermostat. I am not making this up.

If the thermostat is also scorched, you must replace it. If the old wire is braided cotton on rubber icon_eek.gif then you must replace it with a modern heat-proof cable (you can buy immersion cable by the meter in DIY sheds or Electrical suppliers). Old rubber cable will be perished and the insulation may crack or fall off which is very dangerous. You should be able to connect it at the local switch in the airing cupboard. If there is no switch, or the switch is very old and unsound, come back and there are a couple of alternative ways of doing it safely. Do not make a "temporary" joint in the cable, there are correct fittings available for only a few pounds depending what you have got.
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Agile

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PostPosted: Sun Jun 07, 2009 4:09 pm Reply with quote

He is not making it up but its not the metal being soft that is causing the problem.

It also gets black oxide on the surface and its that oxide layer which causes a high resistance and overheating and then arcing.

If the contact surfaces can be cleaned then it may survive but ensure there are no flamable things nearby.

Wait until the wather is fairly warm and move the stat around the scale and see if it turns of in an appropriate setting.

Tony
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mikell

from United Kingdom

Joined: 18 Sep 2006
Posts: 154
Location: Liverpool,
United Kingdom

PostPosted: Sun Jun 07, 2009 4:15 pm Reply with quote

thanks john i get that about the copper ,it became all brittle and grey, and it is braided cotton type so i will change it too.
how out of date is type of wiring,is it from the 80s /90s/life on mars type 70s retro cable?! icon_lol.gif
I know the house had bakerlite black sockets and intertwined black cable ,but had been rewired at some point .just leaving the carcasses in certain rooms unconnected.
cheers guys.

this ol` house, said shakey! lick of paint my ar**! icon_biggrin.gif
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