250l UV Tank

[johnwa]

I have had a 250l horizontal tank installed in the loft, my question is it has two 3kw immersions is one enough to fully heat the tank or is it best to use the two? the tank is also supplied with only one, I had two just in case of a failure.
Thanks for any pearls of wisdom

 

[Johntheo5]

It will take 14.53 Kwh or almost 5 hrs to heat 250L from cold at 10C to 60C with a 3Kw heating element, normally, this element would be installed in the bottom of the cylinder and used to heat the cylinder overnight with cheap rate power, the other element might be installed about half way up the cylinder and just used to boost the temperature by day.
Where are your elements installed?

 

[johnwa]

Hi John thanks for the reply, Either end of the tank about 40cm from the ends, it is a Horizontal tank, John.

 

[Johntheo5]

I should have seen that its horizontal in your original post so the above doesn't apply, so yes it should heat up in 1/2 the time if both are energised together but remember two will draw 26A (at 230V) so if maybe not a good idea if you have a EV charging or using a electric shower or suchlike.

 

[johnwa]

Hi John it's proving to be a bit of a task to work out whats going on! I have set the tank stat to 50 and the Thermowatt immersion heater is set to 55-60 as standard (I have a smart one to go in) but this morning doing a continuity check across the tank stat it shows a short which means the tank temperature hasn't got to where it should be! so either the safety cutout has tripped, the time switch, or the element?
More checks needed me thinks.

 

[Johntheo5]

How long was the cylinder heating on for?, with one or two elements?.
Is the Thermowatt the normal standard supply and how is the other element wired in the system/.
The element(s) is easy to check out, a 3kw will have a resistance of either 19.2ohms (240V) or 17.6ohms (230V).

 

[johnwa]

Hi John the immersion was on from 12.00 to 07.00 with one at the moment, the second 2.5mm feed going in today.
I will check the elements etc this afternoon.
Thanks

 

[johnwa]

I changed the thermostats over same situation the tank stat is still calling for heat.
As the tank stat is at the near bottom of the tank I am wondering if they will ever be more or less the same? and be content with the boiler doing most of the heating?

 

[Johntheo5]

You have a heating coil in the cylinder as well?, can you post a link to that cylinder, you generally don't have both immersion and boiler heating on together, the immersion is normally be a back up for the boiler (normally cheaper) heating or maybe just used during the summer months. If your boiler coil is also on overnight then that should have increased the cylinder temperature to 60C or whatever the cylinder stat is set to.

This what a typical horizontal cylinder migh look like.
View attachment 342028View attachment 342028

 

[Madrab]

Is the cylinder indirect - I.E. is it's primary heat source the central heating? If so then the immersion element is only a back up for when the CH fails and should not be considered it's primary source.

 

[Madrab]

The other issue you have is - it's a horizontal cylinder - sorry but to be direct they really are terrible things.

HW Cylinders were never designed to be on their side by the very nature of how they are designed. Using convection as they do, I've always found horizontal cylinders to very inefficient when trying to heat the whole store and they always struggle to provide anywhere near a full cylinder of hot water.

I never recommend them and opt to fit smaller standard vertical cylinders in tandem.

 

[johnwa]

Hi Madrab thanks for the input and understand the logic behind it, and yes it is indirect, my idea is to use the off-peak times with 1 or 2 immersions and the boiler to do the main heating, I think I am wasting my time trying to get the stats to work at the same temp, I have a smart Thermowatt element to go in and may fit the WiFi temperature control? I think the two immersions will give a better temp throughout the tank top? well I hope so! it will mean both immersions on for half the time as one or set one slightly lower temp?

 

[johnwa]

Hi johntheo5 this is the beast https://www.telford-group.com/product/horizontal

 

[Johntheo5]

This is what you should have, with top mounted Immersion as standard, don't see blank for the second immersion. It gives a reheat time of 35 minutes using the indirect coil, this means the coil is rated at 24.5kw but this would probably be at a 80C boiler flow temperature which you are unlikely to be running at, however, if only running at 65C then there is no reason IMO why you cant heat that 246L from say 15C to 50C (stat setting) in a hour or so except that the boiler is cycling on/off, the coil should be outputting ~ 10kw so shouldn't be a problem for the boiler, is the motorized valve opening?.

You said you swapped the stats around, the stat pocket shown near the bottom is for the cylinder coil, the immersion stat is often in a pocket in the immersion itself that you access by removing the immersion top, where is the (second) stat pocket that you seem to be referring to?

 

[johnwa]

Hi John the second immersion was a special order, sorry to confuse but I swapped the immersion stats over to eliminate any problem. Yes the HW is working as it should John the boiler is set to 70, I suppose I was expecting the immersion to share a bigger proportion of keeping the tank charged I am still a bit confused as to why the Immersion is preset to 60 for 7 hours and the tank stat is set to 50 yet in the morning the tank thermostat is calling for heat, once the boiler is on for some time the contacts on the tank stat open as they should and the valve closes.