Single immersion cylinder not heating during Economy 7 off-peak times

29 Nov 2020
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United Kingdom
Hi, first time posting here.

I’m on an Economy 7 tariff, but up until recently only used it to heat my storage heaters, but never used it to heat water in the cylinder overnight as I just use the electric shower whenever I need it. I had the boost timer to come on at 7pm for half an hour to heat the water so I could do the washing up.

However, the electric shower is broken and am now wanting to use hot water from the cylinder heated overnight to take showers in the bath instead.

I changed changed the off-peak timer setting to come on from 01:30 to 07:00, but woke up to find it hasn’t heated the water at all. I’ve had to resort to using the boost button during peak times to heat the water.

I tested the timer and a ‘Timed’ light would come on when the timer enters the chosen off-peak time.

Unfortunately, I don’t know if the off-peak timer ever worked as I haven’t used it since it the timer and cylinder was replaced.

I have a single element immersion heater connected to a Horstmann Electronic 7 timer

Thanks in advance
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Hi, further to my previous post...

I previously had two wall switches, which was then converted into the Horstmann Electronic 7 timer with one switch.

Also, there is a burn mark on one of the fuses for the Economy 7 set of fuses.

All of my storage heaters have been working the whole time.

I wonder if its just the fuse that’s blown?
Do you know if you have a Dual Element Immersion? I wonder if the Off peak element has burned out, which would explain why the fuse has blown.

Fuses as in at the Fuse box? Could again, be a blown element which has caused the fuse to blow, but if you are not sure, I would strongly suggest you get an Electrician in to check things over and ensure all is well.
Thanks Hugh.

It’s a single Heatrae Sadie Pullin 11” Gold Dot immersion heater connected to the top of the cylinder. From what I can find online it doesn’t seem like a dual element immersion?

Yep, fuses as in fuse box. Don’t know whether it’s also worth mentioning that I live in a hard water area and the cylinder and element was installed over 10 years ago.

Before I contact an electrician, I was also hoping to understand if anyone thinks my current setup sounds about right for someone on Economy 7: cylinder with single 11” element at the top with a Horstmann electronic timer. Does that sound right?

From what I’ve read online, I thought people on Economy 7 should have a cylinder with two elements: one at the bottom for off-peak and one half-way up for the booster. The existing 11” element seems rather short for the cylinder if it’s expected to heat the whole cylinder during off-peak times. Also, I’m not sure why the two switches were changed to one on the Horstmann Electronic 7 timer instead of having the off-peak on a switch which is permanently left on, and another for the temporary boost option.
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Usual practice is, for Economy 7 is, as you've described, a twin element setup. Idea is the bottom element heats the whole tank during the overnight E7 period of cheap rate electricity. Then top immersion is used to top up the hot water outside of the E7 period if it runs low. Your setup doesn't sound right, you would need a dual element immersion to take advantage of the E7, whilst it may be possible to make 2 connections from the Horstmann unit to the one element, I cant see it being good (or safe) practice.

Hard water can kill immersions, pulled plenty out that are encrusted with limescale, (and usually split hence and knackered, hence why they were pulled out!), so after 10 years of use, it's probably overdue replacement! Can you put a pic of your tank up? Not sure what you've got there, and you are correct in saying an 11" immersion usually is fitted in the side of the tank. (This is used in the twin element setup, as the immersions are fitted horizontally, top and bottom.) Top entry (on a slight angle) have 27" immersion that heats almost the full depth of the cylinder.

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