If your IH is modern,it will have an additional overheat device. If it is scaled up, this could be operating.
Solution is to remove IH and clean it up. Also think about a water softener.
Needs doing pronto, IH could be damaged by this.
To remove heater, saw out gasket with a hacksaw blade. Comes out a lot easier.
And score the jointing surface of the cylinder.
There is no real alternative. The new heater can be put back with a little jointing compound on the surface of the cylinder flange.
I have never failed with this. You have to go all the way round and saw all the way through the gasket. You can feel the blade skidding when it reaches the metal. Takes about five or ten minutes. Best to leave as much water as possible in the cylinder to give support to the thin metal. This removal problem is caused by joint compound on the gasket set really hard due to the heat.
When the time come to remove, apply torque both ways alternately. Handle on spanner can be tapped, also WD40 squirted in helps because the gasket is cut away.
Wrap some electrical tape round the hacksaw blade to make a "handle".
You will find the remains of the gasket is stuck to the flange like it was cemented on. Needs a file to clean it off.
The only time this method fails is if some bastard has put jointing compound on the threads of the IH
No. Any water it heats will immediately flow to the top of the tank, limes= cale or no limescale, so there is no chance for a pocket to form.
It's much more likely your element has burst (they don't last many years) a= nd it's trying to heat the water like an electrode by passing current from = the element to the earthed tank.
Have you got a multimeter? If so, this is super-easy to check from outside= the tank.
Isolate the electricity supply to the heater and remove the cover. Put you= r multimeter on the most sensitive resistance mode and measure the resistan= ce between the two contacts connected to the element. This should be about= 19 Ohms (assuming a 3kW element). If it isn't it will most likely read in= finity (or 1) on your meter which means the element is bust.
To confirm this further, put your multimeter on the highest (least sensitiv= e) resistance mode and measure the resistance between the live side of the = element and the earth rod. If this is anything but infinity (or 1) your el= ement is bust and there is an electrical connection from the inside (which = is supposed to be insulated) and Earth via the water.
HTH
Alex
+1
Bollocks. They cease to work by reason of overheating long before things get that bad,
multimeter on the most sensitive resistance mode and measure the resistance between the two contacts connected to the element. This should be about 19 Ohms (assuming a 3kW element). If it isn't it will most likely read infinity (or 1) on your meter which means the element is bust.
resistance mode and measure the resistance between the live side of the element and the earth rod. If this is anything but infinity (or 1) your element is bust and there is an electrical connection from the inside (which is supposed to be insulated) and Earth via the water.
On of the first things I tested. Reads 19ohms, exactly the same as the working element. Hence my conclusion that the element was OK (FSVO OK) and the problem was localised heating where the hot water cannot easily rise to the top because it is surrounded by limescale.
If you've got that problem, then it may be the safety cutout operating before the thermostat has time to respond.
Well then, that cylinder I removed from a neighbour's house a couple of years ago, that was filled halfway up with limescale, must have been a figment of my imagination. Thanks for putting me right, 'arry.
Yes dear, keep taking the dried green frog pills and you will soon feel better.
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