I would get the installer back sharpish.

Is anything overheating and discharging water.

Hi Chaps
Installation of Megaflow tank was about 18 years ago when the house was built! Its only in this month we have had solar PV (electric) panels installed hence the need to heat HW via the daytime free electric.

No discharge of water at all. Just the knocking and banging as the immersion heater heats the water. It stops as soon as the immersion cuts out or the solar control module detects lack of production of power from the panels or some appliance in the home is turned on taking the power. So no mains power is used at all to heat the water - its free! Ok I have to pay for the panels but everything they produce up to 4KW/hour is free for my use.

Oh yes, to note, due to being in an extremely hard water area all our domestic water H & C is via a Harvey's water softener, which has been in work for about 4 plus years now.

Guessing on my part... I feel its scale on or around the immersion heater but the softener should be dealing with that shouldn't it?

Does a water softener slowly dissolve existing scale build up? Which would have been there for nearly 14 years before the water softener was installed and the immersion has never been used before now.

Thanks for your help.

Hi
Sorry for the delay in replying I've been away on a long weekend break!

The immersion heaters thermostat is set to 70-75C, its this high to get as much heat out of the free electric as possible. i.e. the tank heats to a little more than normal but it then doesn't get any other heating until the next day when the panels produce more free electric.

I could turn it down to 65C - 68C  but I may lose out on the hot water stored?

You get paid your feed in tariff whether you use it or export it. If you export it, you get your fits payment plus a few pence.  If you use it, you get your fits payment and save whatever you pay per unit (18p ish).

It makes sense to use it yourself, but only if you're benefitting from it, otherwise it is a waste.

Small scale installs don't have export meters, only fits meters, so there is no way to know how many units left the building and were exported.  A percentage is therefore used to make an assumption how much was exported.  In this case, you get paid an assumed amount to export, whether you do or not, so you're best using it all yourself if you can!

A fits meter is right after the solar inverter and clocks up units generated before you use them or export them.

An import meter registers units used from the grid. (We all have these)
An import/export meter registers both import from the grid and export to the grid.  As mentioned though, most small scale installs will retain a simple import meter, the export assumed from a percentage.

Has the softener been installed from new or added to an existing system.

Was it commissioned properly and is the salt levels maintained regularly.

I agree scale shouldn't be a problem, subject to the above, but the problem still points towards it.

I would take the cylinder out check the inside and the immersion heaters.

Could you change/check the immersion heaters not for a custard as you need a G3 cert but DIY, why not if your competent.

Salt soften the water not guaranteed to dissolve existing scale, so checking the heaters would be my first job, at the same time I'd be checking the cylinder isn't full of scale, especially the lower immersion heater.

Has it got an inert anode had is it checked replaced every 3-4 years.  

A water softener needs to be commissioned to the use/demand and not unheard of to be too low