Thermal store showing temperatures fine but luke warm water??

Hi Folks- our system is a 210L thermal store heated by:
A- 2 x 3kw immersion, never used
B- Thermal solar panel
C- Multifuel Stove (Woodwarm 12kw)

At the moment "C" is the only thing contributing to heating the store and the central heating pump is set to come on at 70c although all radiators are shut down bar one in the bathroom which is non controllable.

The system is 9 yrs old and has worked well - if the lower thermal store temp is over 40C and the upper obviously somewhat higher we have had decent hot water.

But in the last few weeks and say today the lower was reading 47c/60c upper there wasn't enough hot water to do the dishes I had to boil the kettle!

The CH system was drained in 2010 as the bozos who built the house put no antifreeze in the system and the CH pipes on the lower floor froze (300m above sea level in the Cairngorm Mountains), but the guy who then did it just put in 5l of antifreeze from a plumbers merchant and no dedicated "inhibitor" which was all that was in it and allowed it to freeze in the first place. That's the only work that's been done on the system since new.

Can anyone shed any light on what is happening here?

TIA

Found something on the "Easyflow" website which I hadn't considered...the Blending Valve anti scald thing. Ours is a "Resilience ThermaGuard" and it was set to "MAX". I tried the closest tap upstairs and sure enough really luke warm despite the head of the tank showing 55c. So I went and closed and opened the valve half a dozen times and left it back at "Max"...tried the tap- voila!! Hot water again!! I'm assuming this may have been a build up of crud in this valve slowly preventing the hot side from contributing? Either way I'll monitor it from now on.
Does anyone know of any other factors to watch out for that can cause problems? The CH system will get a drain down this summer as the "non controllable" downstairs shower room radiator is getting replaced anyway, and I'll research what to put in regarding antifreeze and inhibitor.

It’s gubbed

ABCwarrior said:

Ours is a "Resilience ThermaGuard"

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ABCwarrior said:

Does anyone know of any other factors to watch out for

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Reading difficulties may be a factor

Helpful replies....on the sherry already no doubt...

Think Shambolic has nailed it though, had to go through the process today again. Looks like a new complete valve is needed as no amount of searching has led me to a replacement cartridge.... Or just bypass the thing altogether and put warning labels over the HW outlets