Immersion heater

Hardware
1

Hi

My hot water system (UK) at home uses 2 immersion heaters which are connected to a standard timer to heat the water in the tank as and when required.

The immersion heaters stop heating the water when the target temperature is reached i.e. 50C in my case (this can obviously be changed by turning the dial in the immersion heaters).

The issue: I do not have hot water at home when all the hot water is used up and therefore I wanted to find out if there is anything I could do to set the heaters working when the temperature drops below say 35C.

This would eliminate the need of the timers and hopefully the water will remain hot all the time.

PS. I have tried setting the heaters to be on 24/7 and the heating to stop when the temperature hits 50C but this has made my electricity bills rocket high. I have all electric and no gas at home.

Any help would be appreciated.

Thanks

2

surely the heater thermostat will already cause the heaters to turn on once the water temperature drops by a certain amount? How big is the tank? It seems odd to have a timer on a water heater…

3

The heater is governed by the timer this is how it is setup hence why I want to get rid of the timer as the water only gets heated per the timer being on or off.

The size of the tank is 180litres.

4

Maybe replace timer and use a sonoff 16A with a temp sensor.
Then have an automation to turn it on via a schedule and if temperature below X

5

That is the plan but I cannot find a temp sensor. I suppose I need a specific temp sensor which would measure the temperature of the water in the tank.

Do you know any temp sensor?

6

Most if not all UK HW tanks have a temperature sensor strapped around the tank - there is a section of the foam cut out so that the sensor can mate with the copper tank.

You could us something like a ds1820 pushed through the foam and attached to the tank. Sonoff tasmoto firmware already has a setting for that and other sensors on gpio 14

7

I agree with going for power switching and temperature monitoring. Then you use a combination of a schedule and presence detection so that the schedule is overridden if no-one is home (IE: no point having it come on ready for morning showers if you have gone away for the weekend or something)

8

Thanks for the reply mate.

This is what my tank looks like. I cannot see any sensor as such.

20171127_212912
20171127_2129122112×3756 2.03 MB
20171127_212939
20171127_2129392112×3756 1.97 MB
20171127_212951
20171127_2129512112×3756 2.37 MB
20171127_212956
20171127_2129562112×3756 2.22 MB

9

The bare metal around the heaters - does that get hot when the water is heated up? You could attach the sensor there.

10

the bare metal around the heaters do not get hot. Are you saying to attach the ds1820 and connect the ds1820 to the sonoff tasmoto which is then connected to the 2 cables from the immersion heater to the timer?

11

You would use the sonof inline with the main supply to the water heater. Then use the aux input to the sonic for your temp sensor. Another way you could do it would be to install a ‘T’ piece inline with the hot water outlet and use a threaded waterproof temp sensor. You can get these from auto parts shops. You would need the ‘T’ right against the tank to get the best reading and it wouldn’t be perfect but at least it is a submerged sensor rather than just strapped to the outside

12

Could you please provide me with the links to the parts I need to get a bit of noob here.

And if possible a rough schematic of how I need to connect everything up.

Many thanks.

13

Can you please check the current rating (Amps) of the heater? I would hate to provide links to electrical equipment that is not rated for the current demand.

I’ll knock up a schematic when I get home. (Currently on my phone waiting for a flight)

14

I’m guessing the bottom heater is for economy 7 and the upper one is the boost. You would connect to the upper one and let the economy 7 heat the water at the bottom during E7 times.

15

well the breaker used for the immersion heaters is MTN116 Hager (http://www.hager.co.uk/product-catalogue/energy-distribution/protection-devices/mcbs/mcb-6a-63a-6ka-type-b/mtn116/46733.htm?utm_source=print)

The immersion heaters are rated at 2.75-3.0kW 240V 50Hz so that gives roughly 12.5A rating.

16

I dont have an economy 7 tariff.

EDIT: I had my timer on and surprisingly the top heater is much warmer than the bottom one. The bottom one is not warm at all.

17

Hi Dave, hope you had a safe flight back. Did you have any chance to look into the schematic and the parts mate?

18

Hi, sorry for the delay, its been a hectic few days. Take at look at these 16A rated Sonof switches with temp sensor:

Its literally just power in and power out (active and neutral wires, with the earth bridged across. MAKE SURE THE EARTH IS CONTINUOUS!) in line with the feed to the heater element.

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image1618×824 56.2 KB

19

Thanks buddy.

Just a quick question. On the left of the drawing I suppose it’s the main incomer, mine is already connected to the timer do I have to remove my timer and connect the sonoff? I would like the timer to be connected in the circuit and not touch it ideally.

Secondly, I have two immersion heaters in my tank and both the cables from the heaters go straight to the timer, do I need 2 sonoff switches or 1 is enough to feed both the heaters? I suppose the wiring in the timer would be different for both the heaters.

Thanks.

20

Yep, that’s the isolator on the left but you can connect to the output of the timer. If both elements are 2.75 - 3kW then you will need 2 sonof switches, but this is good because it will give you more control. The second one can be the model without a temp sensor since you only need one of them for the tank. If you want to keep the timer in circuit it would be best if it can be set permanently on or in manual override so that all control is done by the sonofs and they never lose power and drop off the network