Reposting this from the plumbing forum as it produced nothing of note: Simple all-electric vented hot water system in small flat. Immersion thermostat cut-out kept tripping, a real nuisance as the flat has a tenant. Plumber changed the stat but it didn't fix the problem. Here's the twist: Plumbing was about 40 years old and probably furred up so we replaced the ENTIRE SYSTEM - cylinder (stainless), immersion element, stat and time switch - and it still trips! Element shows resistance of 20 ohms and house smart meter shows it's using just over 3kW - all normal. Any ideas?
Thermostat cut-out with a twist
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My cylinder had a 9-inch thermostat, think element was 11 inches, since using solar to heat DHW were using it all the time, and it kept failing, both tripping out, and burnt wires, had to set it as low as it would go not to trip the cut out, so got it swapped to a 27" version, since then no problems, the immersion however uses between 200 watt and 3 kW depending on the solar available so in the main it has an easy life. This time of year it does nothing. But it does seem the shorter versions have a harder life.
Mother's thermostat cutout was always tripping out, every time she baked cakes, the Aga was heating the water, not electric, but the thermostat cutout still tripped.
Neither of these seems to match what you are saying.
Mother's thermostat cutout was always tripping out, every time she baked cakes, the Aga was heating the water, not electric, but the thermostat cutout still tripped.
Neither of these seems to match what you are saying.
Is the tenant opening it and twisting the temperature adjustment?
Nope. Deffo not.
In the other thread on this it’s been revealed that the temperature Is set to 60 degrees ….. and this needs turning down
And give the tenant Legionnaire's disease?
You won’t unless it’s under 55 degrees
You folk seem to have an awful lot of faith in the 'preciseness' of these figures !
It sounds as if Murdo would say that, say, 57° was 'too high', but niceboy would say that 58° was 'too low'. What, I wonder, would they both say if the temp were set at 57.5° ?
FWIW I’ve come across this very issue in my long career. Turning down the immersion setting stopped the thermal cut out “tripping”
Temperatures lower should not be required, these thermostats are factory set to an appropriate value and should never need any adjustment.
The fail where people turn them up is because they break the thermostat part by cranking it to the max. Usually the same people that believe turning thermostats up high makes things heat up quicker.
The only other options for failure are that
there is some other heating source for this water
these thermostats are defective from new (unlikely here as they have been replaced multiple times)
or there is a shower pump attached and because the header tank is too small, when it's used the pump draws air into the cylinder which causes the element to overheat.
The fail where people turn them up is because they break the thermostat part by cranking it to the max. Usually the same people that believe turning thermostats up high makes things heat up quicker.
The only other options for failure are that
there is some other heating source for this water
these thermostats are defective from new (unlikely here as they have been replaced multiple times)
or there is a shower pump attached and because the header tank is too small, when it's used the pump draws air into the cylinder which causes the element to overheat.
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But it does, turn my TRV head to 22°C when at 17°C, and it will hit 20°C within an hour, set to 20°C it can take 3 hours. With this
I would agree, likely something the tenant is doing. Likely they are fiddling with settings, and if it goes wrong returning it to original setting, I note my own was set to 45°C and the neutral wire showed signs of having a loose connection as some time in the past, but other than putting a spot of paint on the dial to show if tampered with, then to work out what has been done is rather hard. And I did not carry nail paint in my tool kit.
I may be close to a solution. The live feed to the thermostat was discoloured for the last cm or so, with a rather threadbare clump of copper wire stuffed into the screw-down terminal. I'm wondering if there might have been a little resistance here, producing heat that upset the thermostat as the two are so close together. It would only need a near-immeasurable 0.1 ohm to generate 17 watts, which could get quite hot as a point source. The wire was the one part of the system that was not replaced.
So I've cut off the "bad" bit, exposed shiny new copper and screwed it tightly into the terminal. Tenant reports it has been working fine for the last two days. Fingers crossed.
It has taken three visits by a "qualified" electrician and a plumber of 40 years to get this far without finding a solution. I'm hoping my A level physics and lifetime interest in hobby electronics will show them up.
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We have been talking about an immersion thermostat, which I presume has no 'anti-hysteresis' functionality.
That being the case, I would presume that the thermostat will keep the element energised continuously until the water has reached the set temperature - and it is surely the case that nothing (including setting the stat higher) could result in the water reaching that temp any quicker, isn't it?
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I hope you are correct. Good luck.
Yes of course, I have I will admit often wondered about how a cylinder does heat up.
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