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Immersion heater fault

Hi any thoughts or insight into this fault much appreciated. So it's a 3kw immersion heater that's been causing the water to be scalding hot. It also blew a 15 amp rewritable fuse prior to me changing the stat earlier, anyway just had a text saying the water is still scalding and it's blown the fuse again. I'll go and have a thorough check tomorrow but I'm thinking the immerser may be on its last legs and needing completely replaced. Thanks for reading and look forward to reading any replies. 

  • Just to update i got the plumber to fit a new immerser having found really low IR reading between terminals and earth on the old one , my new thermostat was also fried. anyway i thought all good when i left the job this afternoon but just recieved a text saying water still scalding and despite the boost on the economy7  controller having been been off for a few hours the customer noticed the meter spinning fast and isolated the immerser main switch ( old wylex board) . so the only other thing is the E7 controller that can be at fault ,but surely the stat  would cut out at 60 degrees even if the power is on constantly.... as ever all thoughts and advice appreciated.

  • None of that would overheat the water.

    Have you thought about taking a thermometer with you next time?

  • Doh! Is there a three day satellite delay on this forum?

  • My apologies! 55°C doesn't seem particularly high to me. Aren't you supposed to heat to at least 60°C to kill off the bugs?

  • What do you mean by your new thermostat was "fried?" Is it black and burnt? If so, that can be caused by poor cable terminations.


  • It's a funny old life. I was called out today to investigate an immersion heater problem. About a week ago I installed a new thermostat and Timeguard time switch to an existing immersion heater. My clamp meter showed the correct current draw for the 3kW element. The system ran well for about a week or so then the element refused to heat the cylinder water. When I arrived today I found that the supply was indeed getting to the element terminals.

    The element had gone open circuit due to the copper sheath of the heating element having split.

    The immersion heater was supplied by a 15 Amp hot wire fuse. The system has no R.C.D. I am pleased that I checked the earthing previously or the house metalwork and taps may have become live.

    I installed a new titanium sheathed element.


  • Hi Z.

    Not clear - had the fuse blown - or not?

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