Heating water in electric immersion heater with boost function only

to_be_FTB

Hi, I have a cylinder immersion heater and E7 tariff. I don't use much hot water at home atm so I decreased the heating time during the night tariff to two hours. I tried to decrease it more, but then the water was cold in the morning. I was wondering whether I could just heat the water during the night tariff with the top boost heater only to get a smaller amount of hot water (ie set the programmable heating time to 0, and programmable boost to 2 hours during the night). Has anyone tried that? Do would the water remain hot or would it mix with the cold water at the bottom of the boiler? Any other potential issues with this solution?

* edited to correct: a tank/cylinder, not a boiler

grumbler

What sort of heating do you have in your house?

I know very little about E7, but is it really worth having it and heat water with electricity  when you have a gas boiler and gas is about 5 times cheaper than electricity?

canaldumidi

to_be_FTB said:

Hi, I have a boiler/immersion heater and E7 tariff.

Please explain. Are these two different things - a boiler and a separate emmersion heater? If yes, what kind of boiler? Or are you describing the emmersion heater as a 'boiler'?

I was wondering whether I could just heat the boiler during the night tariff with the top boost heater only to get a smaller amount of hot water (ie set the programmable heating time to 0, and programmable boost to 2 hours during the night

Please explain the 'boost heater'. And the 'progammable  boost'.

It might helpif you posted photos of al the various 'boilers, and all the controls.

to_be_FTB

There is no gas at the property, so everything is electric (heating with storage heaters). 

Sorry, I think it's actually not called boiler, but cylinder, so a cylinder with immersion heater, like here:
https://www.emergencyplumber.uk.com/plumbing/cylinder-immersion-heater-stopped-working/

And this is how the timer/controller looks like:
https://www.amazon.co.uk/Horstmann-Electronic-Water-Heater-Multi/dp/B0031SCQMI/ref=asc_df_B0031SCQMI/?tag=googshopuk-21&linkCode=df0&hvadid=256125662130&hvpos=&hvnetw=g&hvrand=16802512636882052887&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1006598&hvtargid=pla-420104141420&psc=1

So there is no gas, water gets heated directly in the tank, controlled by the timer. I can set hours when it heats (usually this would be during the night/cheaper tariff). I can also program time for boost heating which I think only uses top part of the heating element.  

Cornucopia

Actual pictures might be more helpful, but I'm assuming that what you have is an electric cylinder with two elements - one at the bottom and one about half way up.   

In that configuration, the bottom one is the main element, and is powered by the Economy 7 supply.    The middle one is the boost, and is usually connected to the permanent supply, via the boost button.

In the past, I've swapped over the two supplies to the two elements (either for the same reason as you, or because the more heavily used bottom element has failed).   

Depending on the wiring layout and accessibility, that's a reasonably easy job, but as always with electrical work, ensure that whoever undertakes it is competent to do so safely.

canaldumidi

The boost probably uses peak time price electricity (ie more expensive even than standard rate) even at night. The economy 7 cheap rate electricity is MUCH cheaper.

I would only ever use the boost function in emergency.

If 2 hours at night heats enough hot water for you, use that.

I'm surprised reducing the time down to, say, 1.5 hours, results in cold water. Do you mean ALL the water is cold? Or that it runs hot and then cold after a while?

Hot water rises, so even if you only heat half the cylinder (1.5 hours), that hot water should come out first. Of course if you've only heated half the tank, then after a while (ie after 1 or 2 showers), the hot will run out and it will run cold, in which case you know you need to programme 2 hours each night.

to_be_FTB

canaldumidi said:

The boost probably uses peak time price electricity (ie more expensive even than standard rate) even at night.

I do not understand how this would work - all the electricity I use during during the off-peak hours is charged at the lower rate, why would the boost use peak electricity during off peak hours? (I understand that it's connected to the permanent supply rather than off peak only, but if I am using, e.g. a kettle, it will run on the off peak rate during off peak hours and peak rate during peak hours).

canaldumidi said:

I'm surprised reducing the time down to, say, 1.5 hours, results in cold water. Do you mean ALL the water is cold? Or that it runs hot and then cold after a while?

It was not completely cold, but just warmish, too cold for a shower really (with 1 hour of heating). But maybe something went wrong with the settings - I will need to repeat this again, for now I set it for 1.5h and will see what it's like tomorrow.

to_be_FTB

Cornucopia said:

Actual pictures might be more helpful, but I'm assuming that what you have is an electric cylinder with two elements - one at the bottom and one about half way up.   

In that configuration, the bottom one is the main element, and is powered by the Economy 7 supply.    The middle one is the boost, and is usually connected to the permanent supply, via the boost button.

Yes - that's all correct. Sorry - I am not there now. 

In the past, I've swapped over the two supplies to the two elements (either for the same reason as you, or because the more heavily used bottom element has failed).   

OK - excellent, that's great to know. I would not even need to swap over supplies I think, as the controller lets me programme the boost element the same way as I can program the "normal" (bottom) heating. So I was thinking to set the heating time on the bottom element to 0, and the boost to 1-2h during off peak rates. 

Cornucopia

to_be_FTB said:

Cornucopia said:

Actual pictures might be more helpful, but I'm assuming that what you have is an electric cylinder with two elements - one at the bottom and one about half way up.   

In that configuration, the bottom one is the main element, and is powered by the Economy 7 supply.    The middle one is the boost, and is usually connected to the permanent supply, via the boost button.

Yes - that's all correct. Sorry - I am not there now. 

In the past, I've swapped over the two supplies to the two elements (either for the same reason as you, or because the more heavily used bottom element has failed).   

OK - excellent, that's great to know. I would not even need to swap over supplies I think, as the controller lets me programme the boost element the same way as I can program the "normal" (bottom) heating. So I was thinking to set the heating time on the bottom element to 0, and the boost to 1-2h during off peak rates. 

As long as the boost supply really does take cheap rate electricity, it should be fine.     The boost is designed to heat only the water in the top of the cylinder (sometimes there is a baffle inside that limits the extent to which the cold water in the bottom half interferes with that heating).

to_be_FTB

Yes, all my night energy is at an off peak rate. 

But it feels this is exactly what I want - heat some water at the top and minimise mixing with the cold water at the bottom. There is no point heating the whole cylinder if I am only going to use a small amount of water, but I do want this water to be hot. 

Le_Kirk

If it is true Economy 7, the system only allows off-peak electricity through as there is a relay/switch in your meter that switches between two separate circuits, so putting the boost on during off-peak hours would achieve nothing as there is no electricity available on that particular circuit.  We had the same set-up as you for years until we got gas in the village and now run on a gas boiler (although the immersion and E7 is still available for emergencies).  We found the most economical way was to allow the E7 to heat up the cylinder all night and switch itself off when the temperature was reached with the thermostat on the cylinder.