Dual immersion-long element not heating whole cylinder.
- Thread starter shackec
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Johnthe05
Attached is a photograph of the immersion wiring. I cannot easily get to the switch wiring.
I have checked the voltage across the Brown (bath) terminal to Earth; voltage was 233. Then cranked up the thermostat until it clicked on. V across the terminal was 0; and V across the bath to the neutral return (blue) was 239.
I am getting a current flow to the appropriate bath and sink nodes with the relevant dual switch settings so it doesn’t look like it’s a wiring problem.
It seems to me that the problem is most likely to be that which has most often been suggested. The warm water rises, accumulates and then triggers the thermostat to stop heating. The thermostat is the same length as in the original tank so, for some reason it is acting differently.
The immersion heater is a different make from the original so I suppose there might be design differences or the relative configuration of the heating elements is having an effect. Or possibly a stainless steel cylinder moves heat around differently from a copper one(?) Either way it looks as if my problem is inherent in the system that I have.
The only solution I can think of is to install a shunt pump taking hot water from the top of the tank and into the bottom of the tank. I would need to control this with a timer; perhaps linked to the bath circuit so that it comes on when the bath switch is activated; but also limited as to time. Also would need some one-way valves top and bottom. Starting to look complicated!
Attached is a photograph of the immersion wiring. I cannot easily get to the switch wiring.
I have checked the voltage across the Brown (bath) terminal to Earth; voltage was 233. Then cranked up the thermostat until it clicked on. V across the terminal was 0; and V across the bath to the neutral return (blue) was 239.
I am getting a current flow to the appropriate bath and sink nodes with the relevant dual switch settings so it doesn’t look like it’s a wiring problem.
It seems to me that the problem is most likely to be that which has most often been suggested. The warm water rises, accumulates and then triggers the thermostat to stop heating. The thermostat is the same length as in the original tank so, for some reason it is acting differently.
The immersion heater is a different make from the original so I suppose there might be design differences or the relative configuration of the heating elements is having an effect. Or possibly a stainless steel cylinder moves heat around differently from a copper one(?) Either way it looks as if my problem is inherent in the system that I have.
The only solution I can think of is to install a shunt pump taking hot water from the top of the tank and into the bottom of the tank. I would need to control this with a timer; perhaps linked to the bath circuit so that it comes on when the bath switch is activated; but also limited as to time. Also would need some one-way valves top and bottom. Starting to look complicated!
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I found a old SS11 stat lying around and it is 27" long (to my surprise), don't quite know how this can satisfy the 14" SINK element as the bottom 13" of the stat will be in cold water, one might think that the sink element might tend not to switch off sice presumably the stat measures the average temperature over its full length, anyhow, it doesn't matter what I think because this stat worked fine in my daughters Dual Immersion for 12 years.
There is still something not quite right IMO but what??.
You are quite satisfied that the resistance on the element with the brown wire is 20 ohms?
Suggest, 1, switch off the immersion and run off all the hot water, then switch on the bath, leave it on (do not draw off any HW) for say 2.5 hrs, then open a hot tap and run the water into the bath (stopper in) until the HW is exausted, you should then know if the whole 27" has heated or if you have no idea what this amount of water should look like in the bath, run it into a say 5 or 10L container, note how many containers it takes to exhaust the HW and you then at least have some useful info. I would set the stat to 60C, its presently set to 50C?.
2. If the above only results in say 30/35L of HW, I would isolate the immersion, remove the stat wires, withdraw it and measure its length to confirm its 27" long, (sensing rod), if it is, I would buy and install a new one and see how you get on.
EDIT: Apoligies, its no wonder I was surprised since its only 10 INS long (dark garage where I first measured it) but I would still carry out test.
There is still something not quite right IMO but what??.
You are quite satisfied that the resistance on the element with the brown wire is 20 ohms?
Suggest, 1, switch off the immersion and run off all the hot water, then switch on the bath, leave it on (do not draw off any HW) for say 2.5 hrs, then open a hot tap and run the water into the bath (stopper in) until the HW is exausted, you should then know if the whole 27" has heated or if you have no idea what this amount of water should look like in the bath, run it into a say 5 or 10L container, note how many containers it takes to exhaust the HW and you then at least have some useful info. I would set the stat to 60C, its presently set to 50C?.
2. If the above only results in say 30/35L of HW, I would isolate the immersion, remove the stat wires, withdraw it and measure its length to confirm its 27" long, (sensing rod), if it is, I would buy and install a new one and see how you get on.
EDIT: Apoligies, its no wonder I was surprised since its only 10 INS long (dark garage where I first measured it) but I would still carry out test.
Last edited:
Thank you Johnthe05.
Yes, I have lost track of how many times I have tested the resistance of the elements!
I will set the stat to 60 as recommended; and then try the test you suggest.
Incidentally, I had already stripped down the old tank ready for recycling. It occurred to me to look at the old immersion heater which I managed to find. I don't think it has been changed since removal; and the stat setting was at 80! Tank must have been nearly boiling so perhaps this is why the whole tank heated up? Of course no knowing how sensitive the old stat was. After doing your test I will, perhaps, try setting the new stat at maximum and see what happens. (I tried 70 but that didn't do it) It looks as if the new stat doesn't have a setting for 80; hard to tell since it is partially covered with a very sticky sticker. However I will try max and carefully monitor to see what happens.
Yes, I have lost track of how many times I have tested the resistance of the elements!
I will set the stat to 60 as recommended; and then try the test you suggest.
Incidentally, I had already stripped down the old tank ready for recycling. It occurred to me to look at the old immersion heater which I managed to find. I don't think it has been changed since removal; and the stat setting was at 80! Tank must have been nearly boiling so perhaps this is why the whole tank heated up? Of course no knowing how sensitive the old stat was. After doing your test I will, perhaps, try setting the new stat at maximum and see what happens. (I tried 70 but that didn't do it) It looks as if the new stat doesn't have a setting for 80; hard to tell since it is partially covered with a very sticky sticker. However I will try max and carefully monitor to see what happens.
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