Electric Shower Overheating issue

Sleeper12

Bruthal wrote: »

1 pint heating can.
Shower pump running.
Temperature dial set so 10 pints per minute flows.
Heat can empties and refilled 10 times a minute. 10 pints a minute passes through it.

0.5 pint heating can.
Shower pump running.
Temperature dial set so 10 pints per minute flows.
Heat can empties and refilled 20 times a minute. 10 pints a minute still pass through it.

100 pint heating can.
Shower pump running.
Temperature dial set to 10 pints per minute.
Heat can empties 1/10th volume per minute. So it can still heat and supply 10 pints per minute the same as other 2 cans. But it would take a few minutes to initially get to operating temperature, and it would no longer be an instant shower.

In all 3 cases, 8.5kw heat put into water. And that is fixed. No way to increase pints per minute heated by certain temperature.

I hear what you are saying but in real life it doesn't work that way. Please don't ask me to explain it because I can't & you seem to make perfect sense but it still doesn't work that way.
YYou will always get better pressure from a can with a lot of limescale then and new can.
Could the limescale itself come into play? Is it holding the heat better?

All I can tell you is every time an element is charged because of limescale the temperature (water pressure) dial has to be changed.
Not trying to argue & as I say I can't explain it. There must be an unknown factor not in your equation.
Had a guy on electric forum explain to me (he had a formula & everything) that my hot press cylinder can't heat enough water for a bath. He proved it takes 2 hours. My 3.5kw immersion takes around an hour. I have since tested several family members immersions & they are all a little over an hour.

Bruthal

Sir Arthur Daley wrote: »

In old showers this would be true but the ones with phased shutdown elimates this.

To say it doesn't happen with them ones doesn't change what happens with the vast majority of electric showers in use now, and the OPs shower.

Bruthal

Sleeper12 wrote: »

I hear what you are saying but in real life it doesn't work that way. Please don't ask me to explain it because I can't & you seem to make perfect sense but it still doesn't work that way.
YYou will always get better pressure from a can with a lot of limescale then and new can.
Could the limescale itself come into play? Is it holding the heat better?

All I can tell you is every time an element is charged because of limescale the temperature (water pressure) dial has to be changed.
Not trying to argue & as I say I can't explain it. There must be an unknown factor not in your equation.
Had a guy on electric forum explain to me (he had a formula & everything) that my hot press cylinder can't heat enough water for a bath. He proved it takes 2 hours. My 3.5kw immersion takes around an hour. I have since tested several family members immersions & they are all a little over an hour.

OK, your turn to answer.

How many litres per minute from an 8.5kw shower with clean can, and the same shower with can with half volume? Both with identical temperature input and output?

I can explain the 2 hour immersion one if you like...

It takes 2 hours to heat the full cylinder by 65 degrees as example by calculation.

But it's true to say the immersion does it in around an hour. How you ask?

His calculation was very likely perfectly correct. It does however fail to consider....
1. The full cylinder volume is not heated.
2. The top part will reach 65 degrees long before the bottom half.

So neither the entire volume is heated, nor does the part that is heated all reach 65 degrees. Simpler it could not be.

Sleeper12

Bruthal wrote: »

Its likely. But as I was saying, my shower trips its overheat stat after every switch off. I'd say there is some scale built up. But the temperature in the heating can always soars up in any shower switched off from full on. At switch off, flow has ceased, but element still at operating temperature.

Just try switching one off, and back on 20 seconds later. It will be roasting for a few seconds. So I'd say it happens on properly working showers sometimes too.

I know you are getting different answers here but it is limescale. The kettleing noise is the water about tonight boil after you turn it off. The Tco has 2 fuses in it. It is normal for the first one to trip after a shower but it is the 2nd fuse (or both) you hear trip. It trips at a much higher temperature. The 2nd fuse is a last defence.

suirvale

any site for shower spares in ireland plz thanks ,,.

Sleeper12

suirvale wrote: »

any site for shower spares in ireland plz thanks ,,.

What make of shower?

Sleeper12

Bruthal wrote: »

OK, your turn to answer.

How many litres per minute from an 8.5kw shower with clean can, and the same shower with can with half volume? Both with identical temperature input and output?

I can't answer you. Honestly not being funny. Between us we are definitely missing an unknown factor. I'm not saying that you are wrong it looks like you are making perfect sense. That is why I suggest we are missing something.

2011

Bruthal wrote: »

If the element is that badly scaled, it won't transfer as much heat to the water, hence the extra heat transfer to the can and stat.

Exactly.

As Bruthal says the energy input is fixed at 8,500 watts which is 8500 joules / second.
Therefore there is only so much energy available to transfer in the form of heat to the water.

I takes 4181 joules to to change the temperature of 1 litre of water by 1°C.
1 watt = 1 joule / second.
Do the maths.

Bruthal

Sleeper12 wrote: »

I can't answer you. Honestly not being funny. Between us we are definitely missing an unknown factor. I'm not saying that you are wrong it looks like you are making perfect sense. That is why I suggest we are missing something.

Yes, you are saying more water flow is possible with a smaller can. And you keep same temperature.

I'm saying that's not possible. You can not get more heat into water per minute with the same element, no matter what you do.

You stated a can half the size heats faster. But you still neglect the fact that the same amount of water flows through the can per minute. Its true it flows through the can faster. But the litres per minute through it is exactly the same.

It is absolutely not possible to put more than 8.5kw of heat into water when the element is 8.5kw output.

Bruthal

2011 wrote: »

Exactly.

As Bruthal says the energy input is fixed at 8,500 watts which is 8500 joules / second.
Therefore there is only so much energy available to transfer in the form of heat to the water.

I takes 4181 joules to to change the temperature of 1 litre of water by 1°C.
1 watt = 1 joule / second.
Do the maths.

Yes so the element in question can heat 2 litres of water per second by 1 degree.

So in 1 minute it heats 2 litres by 60 degrees. 6 litres per minute by 20 degrees.

Now it won't make any difference what so ever about the size of the heat can. If the can is half the size, it will fill twice as quick, still taking on the same heat per second.

Sir Arthur Daley

Bruthal wrote: »

If the element is that badly scaled, it won't transfer as much heat to the water, hence the extra heat transfer to the can and stat.

If an element cannot transfer the energy to the water due to the scale how can the can and stat get extra heat transfer?

Bruthal

Sleeper12 wrote: »

I know you are getting different answers here but it is limescale. The kettleing noise is the water about tonight boil after you turn it off. The Tco has 2 fuses in it. It is normal for the first one to trip after a shower but it is the 2nd fuse (or both) you hear trip. It trips at a much higher temperature. The 2nd fuse is a last defence.

You would think I was asking the question?? I already answered early in the thread that element scale is likely

The second one is a fuse. It needs to be replaced when it goes. It is the first one which only disconnects half the element, which trips in my one, and many others.

As I said, it can happen in any shower due to residual element heat into heat can at switch off.

2011

Sir Arthur Daley wrote: »

If an element cannot transfer the energy to the water due to the scale how can the can and stat get extra heat transfer?

Agreed, the limescale will reduce the ability of the element to transfer heat to the water.

However the debate is about a different issue.

Bruthal

Sir Arthur Daley wrote: »

If an element cannot transfer the energy to the water due to the scale

I didnt actually say that. I said...

it won't transfer as much heat to the water

how can the can and stat get extra heat transfer?

The element is physically connected to the can. It is not the water temperature it monitors. Its the can outer surface.

The secondary overheat stat is physically in contact with the outside of the can.

Since the limescale insulates the element from the full cooling effect of the water, more heat transfers to the can. Some small amount always does transfer to the can, hence there is a recommended duty cycle. But extra heat does when the element is scaled up.

Sleeper12

Bruthal wrote: »

Yes so the element in question can heat 2 litres of water per second by 1 degree.

So in 1 minute it heats 2 litres by 60 degrees. 6 litres per minute by 20 degrees.

Now it won't make any difference what so ever about the size of the heat can. If the can is half the size, it will fill twice as quick, still taking on the same heat per second.

I said I didn't doubt your reasoning & the figures seem to stack up. But there is something missing from the equation. Either that or shower heating cans are defying the laws of physics.

Every time a new heating can when replacing one caked with limescale is fitted then the pressure has to be increased. I'm not saying this as my opinion, I'm saying this as in this has to be done. I do it, every other shower repair company has to do it & you have to do it.
As I say I don't dispute your figures, I'm saying there has to be something else at play that we are not thinking about.

Bruthal

Sleeper12 wrote: »

I said I didn't doubt your reasoning & the figures seem to stack up. But there is something missing from the equation. Either that or shower heating cans are defying the laws of physics.

Every time a new heating can when replacing one caked with limescale is fitted then the pressure has to be increased. I'm not saying this as my opinion, I'm saying this as in this has to be done. I do it, every other shower repair company has to do it & you have to do it.
As I say I don't dispute your figures, I'm saying there has to be something else at play that we are not thinking about.

That is true. But it is the reverse of what you said earlier. You said it is better with the old can, and clients claim it was better as was. If the new can is fitted, and flow rate has to be increased, then the new can is better, is it not?

That goes along with what I said earlier, that thick scale actually reduces the heat put into the water. It must do, because for the can to overheat, les heat goes into the water.

But the old limescale filled can cant increase heat to the water compared to a new one.

Sleeper12

2011 wrote: »

Agreed, the limescale will reduce the ability of the element to transfer heat to the water.

However the debate is about a different issue.

This isn't really a debate as I say I agree with the logic. I'd be stupid to say the world isn't round. What I am saying is that when you replace a limescaled heating can you always have to adjust the pressure dial. That doesn't say you are wrong. I'm suggesting there is an unknown that has to be factored in

Sleeper12

Bruthal wrote: »

That is true. But it is the reverse of what you said earlier. You said it is better with the old can, and clients claim it was better as was. If the new can is fitted, and flow rate has to be increased, then the new can is better, is it not?

That goes along with what I said earlier, that thick scale actually reduces the heat put into the water. It must do, because for the can to overheat, les heat goes into the water.

Yes the client says older one is better because you need to reduce the pressure for the new can. The old can is much hotter (that's why it needs to be replaced) so there is better pressure.
If the can doesn't get too hot why pay me to change it?

Bruthal

Sleeper12 wrote: »

This isn't really a debate as I say I agree with the logic. I'd be stupid to say the world isn't round. What I am saying is that when you replace a limescaled heating can you always have to adjust the pressure dial.

There is no debate about having to adjust the dial to get the same temp. But that is different that saying the shower performed better with the clogged up can.

Sleeper12 wrote: »

The biggest problem I have after replacing a shower like this (even with the same model is quite often the client feels that the damaged shower was better than the new one. This is because Less water fits into the scaled heating can. Obviously if the can holds only half the amount of water as the new one then it heats the water quicker.

Bruthal

Sleeper12 wrote: »

If the can doesn't get too hot why pay me to change it?

The can getting too hot is because less of the 8.5kw heat from the element is going into the water. Therefore the flow rate needs to be reduced by the user.

So a new can should have a slightly better flow rate, since less heat is going into overheating the can. You even said it yourself...

Sleeper12 wrote: »

Every time a new heating can when replacing one caked with limescale is fitted then the pressure has to be increased.

Sleeper12

Bruthal wrote: »

There is no debate about having to adjust the dial to get the same temp. But that is different that saying the shower performed better with the clogged up can.

I never said I thought the old can was better. I said that the client feels it's better.
I have to try explain to the client that the weaker pressure is a good thing.
LLimescale makes the shower hotter and not colder. Limescale = more pressure. No limescale = less pressure.
I hhaven't a clue how to factor that into physics all I know is that is what happens.

Sir Arthur Daley

Bruthal wrote: »

I didnt actually say that. I said...

My bad i worded my post wrong there im sorry.

The element is physically connected to the can. It is not the water temperature it monitors. Its the can outer surface.

The secondary overheat stat is physically in contact with the outside of the can.

Since the limescale insulates the element from the full cooling effect of the water, more heat transfers to the can. Some small amount always does transfer to the can, hence there is a recommended duty cycle. But extra heat does when the element is scaled up.

I was of the thinking that if an element was so covered in limescale wouldnt the limescale act as an insulator in transferring energy full stop.

Sleeper12

Bruthal wrote: »

The can getting too hot is because less of the 8.5kw heat from the element is going into the water. Therefore the flow rate needs to be reduced by the user.

So a new can should have a slightly better flow rate, since less heat is going into overheating the can. You even said it yourself...

Your not thinking about kettleing. The heat does transfer to the water. Kettleing = boiling water. No limescale the water won't get hot enough to kettle. Limescale & it kettles.

Bruthal

Sleeper12 wrote: »

I never said I thought the old can was better. I said that the client feels it's better.

But you seem to agree with them from your posts

I have to try explain to the client that the weaker pressure is a good thing.
LLimescale makes the shower hotter and not colder. Limescale = more pressure. No limescale = less pressure.

Yes, limescale clogging the shower head makes the shower hotter, because it physically reduces the flow rate.

Limescale on the elements slightly reduces the heat input to the water. How else do you think the overheat stat overheats due to limescale?

Its because slightly less heat goes into the water. And the heat not going into the water is what overheats the can and trips the stat.

The limescale insulates the elements from the waters cooling effect. That is how the can and element overheats. Now if the water is having a less cooling effect, it must therefore not be absorbing as much heat while it is flowing through the can. How then is it getting hotter?

Bruthal

Sleeper12 wrote: »

Your not thinking about kettleing. The heat does transfer to the water. Kettleing = boiling water. No limescale the water won't get hot enough to kettle. Limescale & it kettles.

Kettling can happen in any shower.

I never said heat does not transfer to the water. Nor that this kettling was not a sign of limescale.

The element outputs 8.5kw

Most goes into the water in a normal operating shower. Limescale causes slightly less heat to reach the water during operation. The remainder causes overheating of the can.

I am shocked you dont grasp that. Water cools element, shower works fine.

Scale on element, can overheats. The element still only produces 8.5kw.

So where does the extra heat to overheat the can come from?

Normal operation........8500 watts from element. 30 watts leaks to can as an example. so 8470 watts to water.

Overheat state..........8500 wats from element. 100 watts leaks to can due to limescale insulating element, causing overheat. 8400 watts to water.

No?

Sleeper12

Bruthal wrote: »

But you seem to agree with them from your posts



Yes, limescale clogging the shower head makes the shower hotter, because it physically reduces the flow rate.

Limescale on the elements slightly reduces the heat input to the water. How else do you think the overheat stat overheats due to limescale?

Its because slightly less heat goes into the water. And the heat not going into the water is what overheats the can and trips the stat.

The limescale insulates the elements from the waters cooling effect. That is how the can and element overheats. Now if the water is having a less cooling effect, it must therefore not be absorbing as much heat while it is flowing through the can. How then is it getting hotter?

It's the water that gets hot. Kettleing.
When I say limescaled showers are hotter than new ones I mean the water itself. First thing a shower repair guy does is remove the shower head cause it gives a false reading (a bit like a phase tester over a multi meter) so when I say one is hotter than the other I am talking about without the head on.
It's the water being hot makes the Kettering not so much the can itself.
I ddon't think we'll solve this today but something is missing here & I don't know what it is.

Bruthal

Sir Arthur Daley wrote: »

I was of the thinking that if an element was so covered in limescale wouldnt the limescale act as an insulator in transferring energy full stop.

A new element has water directly in contact with it. This keeps the element much cooler than if it was dry. If dry it would glow red, and in no time, would trip the overheat stat, and the main thermal fuse thing. Im sure you agree with that.

Now if the element is caked in limescale, the water now is not in direct contact with it. So the element gets hotter than normal. This extra heat conducts along the metal element casing, onto the metal can casing its connected to, and the can heats up more than usual. Secondary overheat stat trips.

The can casing itself will be caked in limescale inside also. So the water does not cool it as much as usual either.

Thats my opinion on it at least.

Bruthal

Sleeper12 wrote: »

It's the water that gets hot. Kettleing.
When I say limescaled showers are hotter than new ones I mean the water itself. First thing a shower repair guy does is remove the shower head cause it gives a false reading (a bit like a phase tester over a multi meter) so when I say one is hotter than the other I am talking about without the head on.
It's the water being hot makes the Kettering not so much the can itself.
I ddon't think we'll solve this today but something is missing here & I don't know what it is.

A well now you say the shower head is removed, which is fair enough.

With no shower head on for tests, the clogged heating can will restrict the flow much more noticably than with head on, compared to a clear can, with the temperature dial in identical position.

What you need to do is measure the exact litres per minute, and temperatures. And it will likely be mystery solved.

At the end of the day, anything that slows water flow, will cause temperature increase.


The only factor that gives a better flow rate for identical temperature increase, is a higher wattage element.

I think the mystery is deepened by confusing pressure with flow rate, and hotter water meaning higher heat input to water, which it doesnt.

If the limescale is so bad that it restricts the water flow to a level that has the water temperature hotter, which of course does happen, a client will not think that is better than the clear can, becasue the same conditions can be created with a new shower.

Sir Arthur Daley

Bruthal wrote: »

Thats my opinion on it at least.

I see the logic in it, water being a poor conductor is a big factor too in relation to the element and body being a better conductor.

Bruthal

Sir Arthur Daley wrote: »

I see the logic in it, water being a poor conductor is a big factor too in relation to the element and body being a better conductor.

Yes, water is indeed a poor conductor of heat, but good enough once in contact with the element directly, to keep the element cool enough.

Once a coating of limescale builds up, the heat not going into the water quickly conducts to the can.