Long time ago we had an immersion heater switch which when the water had come up to temperature and the thermostat cut out the heater switched itself off completely. Anyone know where I might buy similar today ?
I've not seen anything like that. I have a manual button to leave it on for
1 hour as well as the economy 7 hours timer. Brian
It's not obvious what you are asking for. The *usual* arrangement is to have a 24 hour timer that defines the periods when you want the heater available, while the thermostat ensures that, within those periods, the heater will be on unless the water is already up to temperature.
You can add a "boost" timer that by-passes the "clock" and gives you, say, 1 hour of heat outside normal times if you actuate it.
Is that what you mean?
I've not come across anything like this. The closest will be the thermal reset button on the heater.
A way of making this work is to use a no-volt style contactor, where the volts for the no-volt relay come from the immersion heater, after the thermostat.
So when it has come up to temperature the voltage driving the heater element drops to zero and the contactor drops out.
Rather than me explain how a no-volts contactor works, JW gives a fair description. Obviously you'll only be using a single phase.
Me neither.
But then you'd have to reset the NVR device every time the water got up to temperatur, or the timer reached the end of the "on" period, before the it could turn back on again, very inconvenient.
What is wrong with a simple boost switch? IF the water gets up to temperature within the boost period, the immersion will cut-off. It's not going to cut back in unless you use a load of hot water and cool the tank ... in which case you probably do want to top it up.
If however you are thinking of boosting it before a bath and don't want to carry on heating after the bath, then just cancel the boost before running the bath.
I thought that is what the OP wanted. Press 'GO' button for a one-shot heating of hot water?
I read it that he wanted the water to come with the timer, e.g. at 6am, and then go off when it reached temperature, but not to bother coming back on again that same day if someone used it all up before the timer went off?
Google "Energy Saver Powerdown", but I'm not convinced there's anything suitable for an immersion heater.
What you are really after is a switch that you activate and which then stays latched on as long as there's a power drain.
A bit like a a no volt contactor as already suggested. But I still don't think the OP has defined his requirements clearly enough.
Sadly the OP seems to have gone AWOL.
But in the OP post there was only a mention of a heater switch and no timer. And used the words, "the thermostat cut out the heater switched itself off completely".
I felt it was perhaps intended for when you might want a bath, press switch, wait an hour, have bath and forget about turning anything off. BICBW
In which case a standard "tumble dryer" type timer is all that is needed. The issue is going to find something pretty that will cope with 3kW.
I don't see where the confusion is arising. He has an immersion heater. He switches it on and when the water reaches temperature and the thermostat cuts the power the power, then stays off. I imagine this would be useful in a household where some members are not careful enough to turn off the immersion before running the bath with the result that the immersion cuts in as soon as the temperature in the tank drops which could be seen as wasteful. Or where the immersion heater is left on unnecessarily.
Yes, but is that really much different to a simple boost timer - hit boost, runs until temperature is reached. Timer times out. The only difference is that if you use a lot of hot water, between the immersion cutting off and the timer timing out, the immersion will come back on for a short while. With a properly lagged tank, that water will still be hot the next time it is needed, so hardly very wasteful ... unless it's an old fashioned bath once a week household ;)
The confusion is that the OP put the word "timer" in the subject line. His description of his requirements doesn't have anything to do with time. He just wants something that detects that no more current is being drawn by the heater and cuts the power.
You could have a relay whose coil is in series with the heater and, when actuated, closes a contact that supplies the power to the heater. You would need a way to reset it, such as a button across the relay contact or a lever that mechanically closes the relay contact. (It would only work if the heater thermostat had reset, but I suppose that would be what is wanted.)
I've no idea what such a device would be called, or whether it is available.
The one we have for our VH does 1,2,3,4 hours extension and so avoids someone leaving it on for several days. Copious hot water is only needed when the place is use so no point in keeping it hot all the time.
It is quite a big saving when almost serious usage is at the weekends. (IOW avoids the expense of a week of keeping the water hot)
It shouldn't happen if people follow the instructions but... (an automatic timed switch is bulletproof)
My Smiths electronic immersion heater timer allows a 1,2,3,?4 hour boost by pressing the boost button 1 to 4 times. Simple. The tank stat overrides at 60C as usual and after the boost period the controller just reverts to normal timed operation. No timed period need to be defined though.
Not sure its something that you can easily buy - most dedicated immersion switches include timers as well to heat at specific times, or to provided a timed "boost" function.
However, what you describe would be easy to achieve with a relay using a circuit like this:
That will then heat until a cylinder stat decides it's hot enough and then turn off the power.
Agreed - the only time element is how long it needs to heat the water, but the time is not a controlled parameter just a variable driven by other factors.
Possibly not - an immersion might cycle on its stat a bit before the cylinder is up to temp (depending on things like how quickly heat disperses in the cylinder and if the immersion is badly scaled up)
Not sure you want a relay coil in series with a 3kW heater?
Easy enough to DIY, see my other post.
Your circuit has a separate thermostat from the one in the heater. Where would it be situated?
My suggested circuit would have a mains relay capable of switching the immersion, with its 240VAC coil across the immersion heater and its n/o contacts in series. To switch on, a pushbutton capable of switching the immersion is wired across the n/o contacts. Or maybe just a pushrod to operate the relay mechanically.
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