Questions about Boiler and Electric Shower

[hohingday]

Hi All,

Happy New Year!

I have recently moved into a new flat and have some questions about my boiler.

It is the first time I have used an electric boiler so I am not sure if this is normal behavior and here goes:
- The boiler only gives me enough hot water for 2 x 10minute showers
- The water seems to run out more quickly during the evening (after 5pm)
- The booster which boils the water doesn't seem to be doing a good job as after using the booster for an hour, I only get 10minutes of hot water.

Is this the norm? Or is something wrong?
(I have attached pictures of the boiler to help diagnose)


Also in my main bathroom we have a 8.5Kw electric shower fitted but it seems to be having a few problems
- The water runs very slow and there is not much pressure, I know it is not the flat as the ensuite shower (boiler water) and taps have strong pressure, is this how a 8.5kw shower should be, as it seems very poor....
- Also my Low, Medium and High settings do not make any difference, the pressure remains constant, very low!
- I am also having a difficult time setting the water temperature and it seems to be hard to get a balance between scolding hot and luke warm, sometimes when I do find the right temperature I randomly get a burst of scolding hot water
- I am assuming there is a problem with the electric shower and I was hoping to replace it with a 10.5kw unit, however I am unable to determine whether I have the right cable thickness to support this, how can I measure it?
(I have attached pictures of the shower and cable)

Sorry for the long winded post and Thanks for your help in advance

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• hohingday
• 4 Jan 2011
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• hohingday
• 4 Jan 2011
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• hohingday
• 4 Jan 2011
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• hohingday
• 4 Jan 2011
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• hohingday
• 4 Jan 2011
• 1

 

[xr4x4]

it looks like you have a direct unvented hot water cylinder with a standard 3kw immersion heater.

what is the timer set to, how often and how long is it on for?

if its set to come on in the morning and you shower at night, the water is already cooling.

 

[xr4x4]

not sure on cable for shower, most likey to be a 6mm2 cable, which limits you to the size of shower you can have.

you would be better to have a thermostatic mixer shower connected to your boiler and the mains water.

mains power showers are up there with gravity power showers.

 

[flameport]

120 litres in the cylinder, so 20 minutes of showering would equate to 6 litres per minute of hot water, which is hardly an excessive flow. Quite likely therefore that a total of 20 minutes showering would use all of the hot water.
This assumes the cylinder was completely hot, and it isn't blocked with years of limescale.

The 'boost' function for an hour won't heat all of the cylinder, so 10 minutes of hot water would be expected.
Probably 3 hours or so to heat the whole cylinder from cold.

For the electric shower, the high/med/low control just changes the amount of power the thing uses. The other knob adjusts the water flow (less flow=hotter water).
If it is erratic then probably blocked with limescale. The only solution to that is replacement.
The cable is probably 6mm, and even if not, there is a lot more involved if you want to fit a 10.5kW model.

Is that a light unit next to the shower? Shouldn't be there.

 

[hohingday]

im not sure what the timer is set to, cant even seem to see one, however we are on economy 7 so I assume its something like 12am - 8am?

We are already short on hot water as there is 3 of us living here, so I think the mixer shower would leave us abit short on water as it stands

I would of thought 120litres would of lasted abit longer than 20minutes.... as two of us use the shower in the evening I guess we are bound to run out?

If it is a 6mm2 cable, I guess the 10.5kw is out of the window as I dont fancy digging up the bathroom, what sort of water flow should I expect from a new 8.5kw unit? (kinda hard to describe i know...)

 

[1john]

shower together, save water.

 

[xr4x4]

there will be a wire coming out of the cylinder, where does it go?

 

[flameport]

The flow rate on any electric shower will be poor when compared to your other shower (which uses mains pressure hot & cold water). This is an unavoidable issue due to the fact the shower has to heat the water as it is used. The problem is worse in the winter because the incoming water will be colder.

The real problem is that the cylinder you have is far too small (120 litres is one of the smallest sizes available). Other than expensive replacement, a possible solution is to change the shower head so that it uses less water
One example: http://www.plumbnation.co.uk/site/m...ter-saving-shower-head---chrome--2-1668-002-/

 

[hohingday]

Haha i dont think the missus will be too pleased that my grand plan is to shower together lol!!!

The wire coming out of the cylinder just goes to the booster and the boiler on/off switch....

Any ideas how I can check the definite size of the shower wiring? All I can see is 300/500V and it is approx 13/14mm thick.

Sigh i miss the gas combi and central heating!!!

 

[flameport]

it is approx 13/14mm thick.

In that case, almost certainly 6mm.
//www.diynot.com/wiki/electrics:cable_types:flatpvccables

 

[Lectrician]

Can you remove the shower cover and take a photo? We can likely tell the cable size for sure then. Personally I think it looks larger than 6mm in the pic, but cannot be sure.

 

[hohingday]

Hi,

Ok so im pretty sure the cable is 6mm2

Replacing the boiler is out of the question at the moment, although I do suspect it needs a service....

So I now need to decide whether to put in a new cable @ 10mm2 or stick with the 6mm2

A few questions:
- What considerations would I need to take if I was to replace it with another 8.5kw unit? (As im pretty sure its not operating correctly)
- If I was to put in a 10.5kw unit, apart from the cable, what considerations would I need to take? mcb, rcb, etc
(I have attached a picture of the fuse box)

I dont plan to do this myself but I would like a clear picture of "exactly" what needs to be done before deciding...

Many Thanks!

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• hohingday
• 5 Jan 2011
• 1

 

[ban-all-sheds]

The important thing to remember with electric showers is that ye cannae change the laws of physics.

The specific heat of water is 4.19J/gK.

An 8.5kW shower will be able to put 510,000 joules per minute into the water.

I've just measured the temperature of the cold water coming into my house at 6.9°C.

If we assume a desired shower temperature of 40°C, that means the water temperature needs to be raised by 33.1°.

The amount of water which can be raised by 33.1° by 510,000J is:

510000 ÷ 4.19 ÷ 33.1 = 3677.3g

So your 8.5kW shower, assuming it's working at 100% efficiency, will deliver a flow rate of about 3.7l/m.

To put that into some kind of perspective:

1) Your 120l cylinder lasts for 20m, and if we use a rule-of-thumb of 2:1 H:C, the shower on that is delivering 9l/m.

2) I've seen 15l/m quoted as the rate at which most people think "Ooh yes - that's a nice powerful shower".

 

[Lectrician]

We need a clearer pic and close up of the fuseboards. (both)

I would like a pic of the inside of the shower to be able to confirm the 6mm theory.......

Your 'boiler' is not a boiler! It is a water heater, a direct, unventedm, mains pressure water heater or 'cylinder'. There is very little to service on them at all - a service will not improve performance. As you only have one element, you cannot even say "perhaps one of my elements is faulty".

Can we have a photo of the controls for the water heater? You say it comes on itself during the night, but you also have a boost?

 

[hohingday]

Unfortunately I am not able to open up the shower at the moment, I will try tomorrow.

I have attached pictures of the fuse boxes.

I cant seem to locate any controls, I have looked all around the boiler and underneath...

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• hohingday
• 5 Jan 2011
• 1

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• hohingday
• 5 Jan 2011
• 1