Hi all, hoping someone can offer some knowledge/experience of immersion heater fault finding.
My parents-in-law's imersion heater stopped working, on inspection I found the time switch had failed open. Also the isolation switch neon indicator was dead. The heater itself had a good resistance of 20ohms, good insulation resistance and good continuity back to the time switch via the thermostat control.
I replaced the time switch and isolation switch, tested and called it a job done.
A month later and the fuse has blown in the CU, re-wireable 15A type. Testing of the circuit didn't reveal a fault. I put it down to a very old fuse and replaced it. It's a Memera CU so unfortunately can't get a CB pulg in for it so had to stick with fuse wire.
A week or so later and the circuit has gone again. Not a blown fuse but the live wire at the CU to the immersion heater had melted, and unfortunately the wire terminal in the fuse slot had fused making that slot unusable.
Tests of the heating element & insulation resistance were all fine. So now I'd put this down to a damaged wire after the initial fuse blow and then a failure of the now weakened wire.
At this point I've left that circuit disconnected, no hot water for the in-laws, as it needs further work and investigation.
I should add that checking the timer (mechanical type) I can tell that the circuit has failed after several hours each time I've had to investigate. So it's not switching into a dead short.
Questions:
1) I have to revisit my assumption of an old fuse causing the blown fuse and damaged wire causing the second failure. A genuine overcurrent is more likely. So why can't I find an insulation failure or shorted heating element?
2) I've not been able to test the thermostat turns off as I've a cold tank and a minimum temperature of 40 on the thermostat. Could the fault be that the thermostat is stuck on and the fuse (and the wire) failed after hours of full load current, where as it would usually only be an hour max until it reaches temperature.
3) the damaged slot in the CU, and the age of the CU make reinstating the circuit as it was impossible. The preferred option is to completely replace the CU and bring it up to regs. However they are in the middle of selling the house and the new owners (if they have any common sense) will rewire the lot. So in the immediate term my suggestion is to put the immersion heater on a FCU from the ring main. Do you think that's sensible?
Thanks for reading and for your help.
My parents-in-law's imersion heater stopped working, on inspection I found the time switch had failed open. Also the isolation switch neon indicator was dead. The heater itself had a good resistance of 20ohms, good insulation resistance and good continuity back to the time switch via the thermostat control.
I replaced the time switch and isolation switch, tested and called it a job done.
A month later and the fuse has blown in the CU, re-wireable 15A type. Testing of the circuit didn't reveal a fault. I put it down to a very old fuse and replaced it. It's a Memera CU so unfortunately can't get a CB pulg in for it so had to stick with fuse wire.
A week or so later and the circuit has gone again. Not a blown fuse but the live wire at the CU to the immersion heater had melted, and unfortunately the wire terminal in the fuse slot had fused making that slot unusable.
Tests of the heating element & insulation resistance were all fine. So now I'd put this down to a damaged wire after the initial fuse blow and then a failure of the now weakened wire.
At this point I've left that circuit disconnected, no hot water for the in-laws, as it needs further work and investigation.
I should add that checking the timer (mechanical type) I can tell that the circuit has failed after several hours each time I've had to investigate. So it's not switching into a dead short.
Questions:
1) I have to revisit my assumption of an old fuse causing the blown fuse and damaged wire causing the second failure. A genuine overcurrent is more likely. So why can't I find an insulation failure or shorted heating element?
2) I've not been able to test the thermostat turns off as I've a cold tank and a minimum temperature of 40 on the thermostat. Could the fault be that the thermostat is stuck on and the fuse (and the wire) failed after hours of full load current, where as it would usually only be an hour max until it reaches temperature.
3) the damaged slot in the CU, and the age of the CU make reinstating the circuit as it was impossible. The preferred option is to completely replace the CU and bring it up to regs. However they are in the middle of selling the house and the new owners (if they have any common sense) will rewire the lot. So in the immediate term my suggestion is to put the immersion heater on a FCU from the ring main. Do you think that's sensible?
Thanks for reading and for your help.