Hot water cylinder only heating top half of tank

[HannahHamilton]

Hiya, we had a new pressurised hot water cylinder fitted a few weeks ago even though its double the size of our last one we are finding we aren't getting any more hot water. So once the tank is full and the emersion has turned off and i touch the tank only the top half feels warm and the bottom half still feels cold. My theory is because the element / thermostat is half way up the tank its only heating to that? which seem pretty crap and a waste of the other half of the tank? basically to where the line is on the picture.

 

[Rodders53]

Who specified the tank?
Who agreed to the suggested tank's installation, checking the spec etc.,.?

Seems glaringly obvious that the immersion is only ever going to warm the top part and is intended purely as 'emergency backup' to the main domestic hot water boiler system that heats via the cylinder's coil.

As you have a solar boost diverter in the home, a different tank should have been specified/chosen/installed with an immersion near(er) the bottom of the tank to make use of that 'free' energy at certain times of the year.

 

[HannahHamilton]

Thank you for you reply. We never really discussed the tank with our plumber he said just said he would get us the 180L one that would fit, the location of the element would never have occurred to us before that. He knew all along about the solar I boost. I have emailed him to raise the issue. pretty annoying.

 

[Johntheo5]

A pity but have a look at the facts.
What is the kw output of your solar array?, have you battery storage?, can you get paid for export?.
what is your daily HW usage? You can get the exact immersion volume by measuring the height to the cylinder top and the total cylinder height.
If you assume 75L, and assume you use that vol/day at 60c (=125LPD at 40C) then that will soak up 4.4kwh/day. You could consider installing a destratification pump, shouldn't cost a fortune and would only require very low power.

 

[HannahHamilton]

I think its bout 4kwh i want to say (but that could be massively wrong). No no battery storage or export - basically we lease our roofspace for free PV Panel, any electricity as we generate we can use at that time (but can't store it) any left over get given to the company and they sell- that why the solar iboost works well for us.
Not sure about the daily allowance but that half a tank isn't enough. e.g. last night the kids had a bath (only 1/3 of a full bath) then i had a shower and washed my hair and at the end of that we had run out, then my husband had to shower in the cold!

What is a destratification pump? does it circulate the hot water around the tank?

 

[SpecialK]

You can turn the stat right up on the immersion but be aware that the hot water will get to about 65 degrees! You could have a TMV fitted to the outlet to mix it down to 40 ish. Such a shame it doesn't have a bottom immersion.
If you still have excess solar you could fit an AC coupled battery (expensive) or run an oil radiator off the other iBoost output in the winter?

 

[HannahHamilton]

Thanks, yeah i turned the value up to 65 already to get as much as we could out of it. Ive contacted my plumber, i don't believe he made the right recommendation in choosing that tank knowing how we were planning om heating our water.
But good recommendation on using the 2nd outlet for something else. Thank you.

 

[Johntheo5]

You could heat the water to at least 75/80C without the immersion safety stat operating but would have to install a TMV as above, you said earlier that you ran out of HW fairly rapidly, was this because you are just using the Iboost to heat the water with no mains electricity or bottom coil heating?
Does your system tell you how much energy you have diverted?
Yes, a destratification pump recirculates the water around the cylinder to mix and give one temperature.

 

[lostinthelight]

I can get nearly 200 litres of hot water from a pressurised cylinder that has solar boost by fitting a secondary pumped return

 

[Johntheo5]

What make/type/head pump are you using?, these bronze bodied pumps don't come cheap?

 

[lostinthelight]

It was a Grundfos comfort not sure of the model unless I dig out the paperwork.. I thinks it was around 150 quid but when the alterative is only 1/3 of a tank then its money well spent

 

[Johntheo5]

I found the data sheets, seem to circulate ~ 5LPM at a 1M head which should be fine for destratification, how is yours installed, pumping direction etc and is there a non return valve installed? how often does it run?. there is a timer on some of these.

 

[HannahHamilton]

Ah thats promising... Ah okay, does it go into the tank directly? Can you set it up on a timier (e.g. Just when its heating) as you dont want it circulating after say you had a shower as it will cool down the rest of the tank?

65 is high as i can set it.

Im not sure i know those answers sorry . At the moment we don't have a timer on it as its quite sunny so we are juat using the iboost as much a possible.

 

[Johntheo5]

I don't have any personal experience of destratification and there is surprisingly little info floating around but obviously some form of control is required, @lostinthelight may point out the correct installation/running procedures.

Can you post the exact details of your cylinder as per attached label, can then see where (if) the secondary return is positioned as can possibly use this as the hot supply to the destrat pump.

 

[SpecialK]

What about fitting a willis external immersion to the hot water loop - this would require some kind of circuit to bring your circulation pump on.

Have you checked how much gas you used during the summer last year for hot water? Is it worth spending any more money?