Immersion troubleshooting - is there anything else I can test
- Thread starter aetos
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- immersion heater
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The original immersions with the externally mounted hi limit (safety) stat only had a control thermostat as was the case no doubt with this installation, the last immersion I changed had this (now) combined control and hi limit (safety) stat so no requirement for two safety stats, one of my relations HW cylinder started boiling over recently, I found the external hi limit stat which had only been glued to the immersion boss had become detached and wasn't in contact with the immersion boss, I replaced it with the combined unit.
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Good description here from JW of how both stats work, in case anyone is in any doubt that there isn't a separate set of contacts. A electric shower thermal cut out (TCO) use two of these discs (its called a duo disc), one, set to 48C, is self resetting, the other, set to 75C, does not reset, the TCO must/should be replaced, you can see one of the discs below, the other is behind it but I don't know if there are two separate sets of contacts.
Thanks all for the further replies to this thread, very educational!
Not sure if this should be a new thread but - It's still occasionally cutting out for no obvious reason. I left the immersion on all day last week and it was grand; I had it on for 30 minutes yesterday and turned it off at the switch, then when I went to switch it on this morning it had cut out again. This keeps happening which suggests a problem somewhere?
Not sure if this should be a new thread but - It's still occasionally cutting out for no obvious reason. I left the immersion on all day last week and it was grand; I had it on for 30 minutes yesterday and turned it off at the switch, then when I went to switch it on this morning it had cut out again. This keeps happening which suggests a problem somewhere?
Do you mean the overheat protection had tripped?
Not really an electrician then?
If the immersion is overheating, this is very dangerous. You need to replace either the internal thermostat, or the entire immersion heater.
Usually the internal rod thermostat is quite easy to change.
Edit
It's the thing with the blue top in your photo.
Actually, it does not look very old. Why would it have gone wrong? Perhaps it is incorrectly wired. Turn the pointer down to 55C and test the temperature of the tapwater with a thermometer.
The thermostat should click when you adjust it higher or lower than the temperature of the water. Use your multimeter to verify that the supply to the element goes off when the thermostat is set lower than the water temperature.
Is the cylinder heated by anything else? A boiler, a stove, a coal fire?
Usually the internal rod thermostat is quite easy to change.
Edit
It's the thing with the blue top in your photo.
Actually, it does not look very old. Why would it have gone wrong? Perhaps it is incorrectly wired. Turn the pointer down to 55C and test the temperature of the tapwater with a thermometer.
The thermostat should click when you adjust it higher or lower than the temperature of the water. Use your multimeter to verify that the supply to the element goes off when the thermostat is set lower than the water temperature.
Is the cylinder heated by anything else? A boiler, a stove, a coal fire?
Last edited:
1. Another thing to consider is limescale. The bottom of the heating element is usually quite close to the base of the cylinder. If there is significant limescale build up this can mean the bottom of the element is in limescale rather than in water, which can cause it to overheat. Once it overheats it will trip the thermostat.
2. If you can remove the immersion heater (the whole thing, not just the thermostat) you can generally syphon / scoop out most of the limescale through the immersion hole. Its not easy and very fiddly to do. Stir up the water and syphon out as much as possible hoping it takes a lot of the limescale with it. For the last bits a wet vacuum is ideal. Poke the hose down into the cylinder before it is completely dry and suck up the dregs. Without a wet vacuum it can be done with a small cup / jar FIRMLY fastened to some sort of pole and a lot of poking about. If you feel up to it you could drain the cylinder the disconnect and up end it. Not for the faint hearted given how difficult it may be to undo some of the connections.
3. Alternatively, change the cylinder.
2. If you can remove the immersion heater (the whole thing, not just the thermostat) you can generally syphon / scoop out most of the limescale through the immersion hole. Its not easy and very fiddly to do. Stir up the water and syphon out as much as possible hoping it takes a lot of the limescale with it. For the last bits a wet vacuum is ideal. Poke the hose down into the cylinder before it is completely dry and suck up the dregs. Without a wet vacuum it can be done with a small cup / jar FIRMLY fastened to some sort of pole and a lot of poking about. If you feel up to it you could drain the cylinder the disconnect and up end it. Not for the faint hearted given how difficult it may be to undo some of the connections.
3. Alternatively, change the cylinder.
OP,
As suggested earlier - replace the IH.
As suggested earlier - replace the IH.
Live is fed to the immersion through the thermostat, then the incorporated overheat stat then the additional overheat thermostat.
From what you say I think
It is a new thermostat that you have fitted
The additional overheat stat keeps tripping.
Seems that this additional stat is tripping at a lower temperature than it should so I would disconnect this and put the brown wire from the heater element straight into your new stat.
From what you say I think
It is a new thermostat that you have fitted
The additional overheat stat keeps tripping.
Seems that this additional stat is tripping at a lower temperature than it should so I would disconnect this and put the brown wire from the heater element straight into your new stat.
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