I would certainly replace any old radiator valves, copper pipe will last many years assuming you have not had any problems with it so far.
There were some really dodgy pipes around after 1965 when Rhodesia declared UDI and cut off the supply of copper but by now they should have shown up if you...
That's not a lock shield I think it is a thermostatic one with the head removed and the blanking cap fitted, if fully screwed down it should depress the pin and close the valve. Possibly someone just put the cap on loosely to allow the valve to pass water, a bit odd!
I assume you have tried new batteries?
Many new batteries come with a sticker that needs pealing off (it has a bad taste I understand to stop kids swallowing them) my Mrs almost got caught putting one in without pealing it recently.
Update if anyone interested.
Went with a Manrose MF100T.
Old vent on wall now redundant.
Spent the best part of a day wheedling the flat duct through the pitched roof and through the soffit, but working fine now!(y):giggle:
Have you checked to see if it has a battery on the door obstruction sensor, mine although not your sort has a sensor bar on the bottom of the door when the battery runs down it fails to close.
Looks like asbestos cement to me going by the thickness and the slight dimpled effect on the rear section, rather than AIB.
You might want to dump the hoover but otherwise I would not worry too much I assume you took it out in more or less whole chunks, so very little risk I would think. (y)
The advantage with brick sets is any movement is taken up whereas any solid surface will crack.
You could try laying paving slabs on top but unless it is fairly level the slabs will soon end up running out of line. I had one patch which I laid on a bed of wet cement over the old concrete but...