Hot water cylinder losing heat too fast

[mpooley]

first thing you want to be checking is what DCawkwell suggested

to be honest I did think that this was the most likely myself.
I checked the indirect coil pipework and that is cold.
leaks! well I can't think where one would be that I haven't noticed.
unless its in the concrete slab I'm sure I would have noticed.

And if it is in the slab god knows how i'd find? god or a good plumber lol

thanks mate

 

[mpooley]

Aha! if your sensor is the same one controlling the heating your cylinder may not ever get properly hot.

The heat is introduced somewhere in the cylinder, and the hot water nearly immediately rises to the top (hot water is lighter than cold water). This forms layers of water at decreasing temperature down the cylinder, which is known as stratification.

You need to make sure that the sensor controlling the heating is placed somewhere lower on the cylinder. Then you will heat all of the cylinder above this point.

If you're switching on the immersion, the sensor at the top will very quickly register 60 degrees but just a couple of inches lower down the water may be near room temperature. So there will be very little hot water in the cylinder at the point you turn it off.

Attach another sensor 9 inches lower and you'll see the effect.

What I can't understand is why the cut out is operating then? could that be faulty? I mean if the top gets too hot before the whole tank is hot enough and the cutout operates, It wont ever get hot then whatever I do!

can I disable the cut out maybe?

BTW you want to get into coding if you are interested. I love it !

 

[mogget]

The immersion should be controlled by the immersion stat. If these are set too high, the cutout can operate. I would leave it set to 60 degrees. The immersion will heat the water at the top of the cylinder first, then lower down. It's possible that the wrong length immersion stat is fitted (or indeed the wrong length immersion heater), or that it's faulty. You can fit a new stat without draining the tank (easy job), and yours should have a 27" immersion heater if it goes in from the top.

If you heat the water fully with the immersion heater, so it cuts out on it's own stat, the water should stay hot overnight. If not something else is wrong!

Might be worth insulating the vent pipe, and as said check for hidden leaks / stray convection currents.

 

[gas112]

Well its simple, tie the ball valve up overnight and see f water level drops if it does you then know its leaking under the concrete slab

 

[mpooley]

Well its simple, tie the ball valve up overnight and see f water level drops if it does you then know its leaking under the concrete slab

good idea i'll try that as soon as I can.

 

[mpooley]

The immersion should be controlled by the immersion stat. If these are set too high, the cutout can operate. I would leave it set to 60 degrees. The immersion will heat the water at the top of the cylinder first, then lower down. It's possible that the wrong length immersion stat is fitted (or indeed the wrong length immersion heater), or that it's faulty. You can fit a new stat without draining the tank (easy job), and yours should have a 27" immersion heater if it goes in from the top.

If you heat the water fully with the immersion heater, so it cuts out on it's own stat, the water should stay hot overnight. If not something else is wrong!

Might be worth insulating the vent pipe, and as said check for hidden leaks / stray convection currents.

it's a newish 27inch heater have set water to 60 now and see what happens.
Vent pipe is lagged. If it's not all that it looks like a leak but I bloody hope not!
How would I ever find it?

 

[Marky_Sparky]

I know this is an old thread but I found it as I had the same problem. Despite the water being very hot one day by the following
morning there was no heat at all. We have a solar PV system that heats the water via the immersion heater when there is excess electrical power available.
So all though summer we have free hot water, it took a while to realise that the heat wasn't being retained very well.
I did all the checks mentioned on this thread over a long period of time even put a longer immersion heater in to help.
The hot water cylinder is foam insulated and I have added another jacket and insulated all the pipes. I used a USB temperature data
logger and could see the loss clearly, it was an exponential shape but for comparison I chose to measure the loss from 50 to 40 deg C which was 3 hours originally.
The additional lagging and longer heater improved this to around 5 hours.
The Coronavirus lockdown got me looking at the problem again. I found some talk about a heat trap which stops the cold water from
the pipe system displacing the hot water in the tank which is what I suspected was happening.
The simplest heat trap is a U section of pipe in the pipe that leaves the top of the cylinder it can also be done with simple commercially available valves.
As I had some pipe and fittings I made a 200mm deep U section to add to the outlet at the top of the tank.
We now have warm/hot water overnight which I'm hoping will be hotter when I get some new pipe insulation fitted.
The 50-40 degree temperature drop now takes 9 hours.

 

[denso13]

As I had some pipe and fittings I made a 200mm deep U section to add to the outlet at the top of the tank.

If this is part of the open vent it should rise continually from the top of the cylinder. A "U section" should not be there if so. A pic would help.

 

[Marky_Sparky]

The information I found shows the heat trap between the top of the cylinder and the rising part of the open vent.
As I had no room directly above the tank I have put the U section rather lower than ideal as can be seen in the picture. The bottom part of the U is out of sight.

 

[denso13]

That really should not be there. The pipe from the top of the cylinder is the open vent and must rise continuously.

 

[Marky_Sparky]

Thanks, what problems will it cause?, this is what I found
https://en.wikipedia.org/wiki/Heat_trap

 

[denso13]

this is what I found

There an no UK links on that Wikipedia page.

From the relevant British Standard "An open vent pipe rises from the top of the hot water storage vessel to a point above the water storage cistern, into which it is arranged to vent. Explosion protection involving no mechanical devices is provided by the open vent and the cistern."

Any air build up has no way of escaping in your set up.

 

[Gasguru]

The Wikipedia article (poorly edited) has been created from a document by ESBE (a heating and plumbing manufacturer) and does not refer to traditional vented cylinders.
The outlet from the top of the cylinder should rise slightly from the horizontal and then join the vertical vent/feed pipework...it must allow the cylinder to boil in case of a fault.
In addition I suspect your taps splutter from trapped air in the cylinder.

 

[Marky_Sparky]

OK thanks, is there any other way of stopping the heat loss?

 

[JohnD]

insulate the cylinder, and the pipes rising upwards from it.

In your case, if you take out your "U" and restore the near-horizontal piece (it should slope very slightly so that air bubbles will escape upwards) most of the heat will be in the horizontal pipe, and the vertical pipe beyond it will be slightly warm. There is not much convection in a pipe unless it is larger than found in a house.

A bit of foamed plastic pipe lagging (the "byelaws" or "regulations" grade is thicker and better, if it will fit) will do the trick. Your pipes are probably 22mm. Measure to check. You can cut it with a breadnife. Mitre bends, and tape tightly to prevent sagging or gaping open, especially on bends.

The "economy" type is thinner, and sometimes flimsy enough to get worn and damaged. Climaflex is a good brand. The plastic foam is quite stiff.

https://www.wickes.co.uk/search?text=pipe lagging

https://www.ebay.co.uk/sch/i.html?_from=R40&_nkw=pipe+lagging&_sacat=0&LH_PrefLoc=1&_sop=15

It is sold in hardware stores in early winter, but there is not much demand in warm weather.