Electric water cylinder - What is normal?

[swa110w]

BACKGROUND:
I have an electric cylinder boiler, which is in my airing cupboard, and heats the water for my taps only, as I do not have central heating.

The boiler comes on periodically in the early hours of the morning, when my Economy 7 night-time rate kicks in. It does not come on during the day unless I switch it on myself (say, to have a bath).

A couple of weeks ago, I noticed that the boiler seemed a lot noiser during the night. It was still working correctly, as my water was hot and plentiful, but the noise (which sounded like a very loud kettle) was getting a bit distracting.

So I got a plumber in, who swiftly diagnosed that the immersion heater was on it's last legs, and fit a new one. They got everything going again, and things were seemingly back to normal.

THE CURRENT PROBLEM:
However, whereas my previous immersion heater used to come on for about an hour (as soon as Economy 7 kicked in) and then would be pretty silent for the rest of the night, this new one kicks in at the same time, but continually switches on and off, presumably as it reaches temperature.

This is quite intermittent and it will switch off for a few minutes, then on for a few minutes, then maybe off for a few seconds, then on, etc. I'm not sure how long this goes on for, but I have woken in the middle of the night to find it doing this.

Also, whilst not as noisy as the original immersion heater when it began to break down, this new immersion heater still seems pretty noisy when heating the water. I daresay this could be me being oversensitive to the noise now though!

SUMMARY:
Now it could be that this is normal behaviour, but my problem is that I'm not experienced enough to know what is normal! I'm sorry this has been such a long query, but to summarise:

1. How frequently should the immersion heater be firing and how long should it stay on for?

2. How come the behaviour of the new one is different from my old, admittedly worn out, immersion heater? Is this new behaviour more efficient?

3. How noisy should an immersion heater be?

 

[JohnD]

is the element at the top of the cylinder, or at the bottom?

Did you notice how long the new one was before it went in?

What sort of insulation is on your cylinder and the pipes around it?

What is the temperature of the water?

Have you checked that none of your hot taps is dripping?

When you say the immersion heater was replaced, you mean one of these,

which fits into a hot water cylinder?

 

[swa110w]

is the element at the top of the cylinder, or at the bottom?

The element is at the bottom of the cylinder.

Did you notice how long the new one was before it went in?

I'm afraid not. I was in another room whilst the work took place.

What sort of insulation is on your cylinder and the pipes around it?

The cylinder is surrounded by a thick (2-3") green solid foam insulation. None of the pipes around it are insulated.

What is the temperature of the water?

I'm afraid I don't know the exact temperature, but it is about what I would expect from a hot tap. I couldn't hold my hand under it for long.

Have you checked that none of your hot taps is dripping?

Yes, I am almost certain that none of the taps are dripping.

When you say the immersion heaterr was replaced, you mean one of these, which fits into a hot water cylinder?

Yes, that is the type of immersion heater I am talking about.

 

[swa110w]

Did you notice how long the new one was before it went in?

I take it back - I know exactly what went in, as it still has the label on it!

It says:

IMMERSION HEATER
11" SUPERLOY / 800
COMBINED THERMOSTAT & SAFETY CUT-OUT FITTED

 

[JohnD]

If it is at the bottom of the cylinder, going in through the side so that it lies horizontally, then it will tend to come on for several hours in the evening when the Economy 7 timer comes on. Assuming you have used quite a lot of water, it will run continuously until the cylinder is fully hot.

However, if you run the taps for a sink or to wash your hands, an equivalent amount of cold water will come into the cylinder at the bottom. The thermostat on the element will detect this, and will turn on the element.

The element will heat the new, cold water until it reaches temperature (this takes about the same time as an electric kettle would take to heat the same amount of water, I suppose ten minutes for a sinkful, something like that). Once it is back up to temperature it will switch off again until you run another hot tap.

The foam insulation round the cylinder will keep it hot enough to use for 24 hours, but any heat lost from the pipes round the cylinder (especially ones coming out of the top) will cause the element to switch on to replace the lost heat. Additionally, since you say the pipes are not insulated, I expect you run a kettleful of extra water out of the cylinder just waiting for the tap to run hot (since you are replacing the cold water in the pipes).

you can get plastic foam pipe lagging in "sleeves" that fit round the pipes, if you estimate about £1 per metre that will be near enough. You can get it in any DIY shed or plumbers merchant. the common sizes are 15mm (basin tap pipes) and 22mm (bigger bath tap pipes). It is available in two qualities, the "BS" stuff is much thicker and is to be preferred, provided your pipes are not tightly squashed and it won't fit. You can get matching plastic sticky tape to fasten it but it fits the pipes well. You can paint it with emulsion if you really want to.

It is particularly important to insulate pipes in unheated areas like lofts, wall cupboards and under floors where they get very cold.

The foam pipe insulation is quite stiff and lasts a long time. I would not normally buy it by post as it is so bulky that P&P will put the price up. It is very light and easy to carry

 

[swa110w]

Cheers John, for that excellent reply.

The only thing I'm having trouble understanding is why my boiler is coming on intermittently, despite no water being used.

Let me explain...

I live on my own, so in a typical day, I might have a shower, wash my hands a few times, wash the pots and that's about it.

My Economy 7 doesn't kick in until around midnight, when I am usually in bed, and therefore not using any water. I will then hear it go on and off for the next hour or so (and possibly later, I am usually asleep!).

Would this intermittent behaviour be due to the heat lost from the uninsulated pipes? This never used to happen before I had it replaced. I know they have chipped out a bit of the insulation foam when fitting the new immersion heater, but surely not enough to make a big difference? And yes, there does seem to be a bit of a lag before the hot water comes out of the tap - I wouldn't say a kettle full though.

I'm just puzzled why my old one would come on solid for approximately an hour, whereas this new one comes on intermittently for longer.

 

[JohnD]

might be a more sensitive thermostat, might be that the orientation of the new element puts the stat lower in the water, might be that it is winter and the incoming water is colder, might be that the thermostat is set higher (you can adjust it under the plastic cap, with the electricity turned off). Your new element is a good-quality one that should last well.

I also have a foam-coated cylinder but I put a red insulating jacket around it as I had one spare. I also used lots of foam pipe-lagging so my airing cupboard is a bit on the cold side now

One day, turn the immersion off and see if you are short of water the next day. Also feel all the pipes. Heat will rise upwards when it can. Any pipes that feel warm are losing heat. As well as a dripping tap there is a chance of a leak.

 

[swa110w]

John - this is superb advice, thanks every so much.

All of those possibilities seem reasonable enough, and if this seems like relatively normal behaviour, then I am happy to leave it as it is. I've had a look under the cap, and the thermostat appears to be on the highest setting.

I have had the immersion heater off on one recent occasion. Although I didn't try having a shower/bath or anything (for the obvious reason), I was not short of water - it just ran luke warm, getting colder throughout the day. Is this what you meant?

I haven't got access to much of the pipework to be honest, but having a quick feel now, the pipe that goes in at the top of the cylinder is very warm (I dry my towels on this!).

Once again, thanks very much!

 

[JohnD]

as the element and the stat are at the bottom of the cylinder, I can't see it needs to be at max temp. all the water above it will be hotter, so I would go for a stat setting of 55 degrees or maybe even 50. No need for it to be above 60 as it will scald. The cooler it is the less heat it will lose.

If you have a very small cylinder and have to mix hot and cold to fill the bath, then it needs to be quite hot.

There will be someone along in a minute telling you Legionella can survive 50 degrees in a closed copper cylinder. I think it grows up to about 45 degrees.

 

[Bahco]

There will be someone along in a minute telling you Legionella can survive 50 degrees in a closed copper cylinder.

Here I am.

Thermostat should be set at 60 minimum.

 

[swa110w]

If I were to change it, it's difficult to guage what temperature it actually is, as the dial has no numbers!

All it has is a + at one end (where it is currently) pointed and a - at the other.

Can anyone translate this to an actual range?

 

[JohnD]

above 45 they stop multiplying and start dying.

most of the cyl will be stored water hotter than the stat setting

the incoming water will (should) be too cold for them to grow

p.s.

a thermometer is what you need

 

[Softus]

Please...

1. Switch off the immersion at the DP switch.
2. Remove the cover.
3. Take a photo of the thermostat and post it here.

 

[swa110w]

Softus, this is my immersion heater with the cap removed. I'm afraid that's the best my camera can do. You can't see it very well, but the arrow is pointing to the left, at the "+".

Immersion heater (cap removed)

• swa110w
• 26 Nov 2008
• 1

Immersion heater (cap removed)

JohnD, this is the top of my cylinder. As you can see, the pipes are uninsulated, and it is that pipe coming out of the cylinder which is very warm. It gets cooler where it turns vertical.

Uninsulated pipes at top of cylinder

• swa110w
• 26 Nov 2008
• 1

Uninsulated pipes at top of cylinder

 

[Softus]

Softus, this is my immersion heater with the cap removed. I'm afraid that's the best my camera can do. You can't see it very well, but the arrow is pointing to the left, at the "+".

That's a good picture in the circumstances.

It looks like a Cotherm 'stat - I tend to set those at 2/3 across the scale towards the "+". In other words, I would rotate your dial about 60° clockwise. Maximum certainly isn't correct, and you can afford to experiment as long you don't get blase and forget to switch off before removing the cover.