When we did new build used tile lathe 25mm x 50 mm also full silicone joint to any edges touching wall before been tiled.
If chip board floor 2 -100mm x 25 mm batterns under bath feet.
If nothing out of prv or condensate waste and no obvious leaks on boiler , and you have re pressured a number of times look round system.
Rad valves are a favourite.
Any buried pipework?
As above turn off.
We were subcontractors to a specialist insurance contractor for 12 years.
Most of the water disasters we saw were unoccupied property's with water left turned on.
Once saw a beautiful 6 bed house on banks of Humber totally wrecked.
Ball valve in heating tank froze split and...
Yes that's the air release valve (Yorkshire rv35)
Has a screwdriver slot but regularly need grips instead.
That's a Dowty washer in it they sometimes leak for fun.
Got my sister stopping for weekend (she's a Dr of horticultural garden designer & lecturers for R H S)
Apparently work on around 25 cubic ft per tonne.
Depending how dry/damp it is.
I take it it's dripping through the shower head not a leak on connecting pipework?
What type of system tank feed or pressurise/combi?
If latter ive seen taps & shower valves pass later in evening as water pressure rises
Passed motorbike test on a 250 Suzuki super six.
Learned to drive in a 1967 mini cooper, also drove the firms Thames 400e van with 3 speed column change!
Notice this some time ago we use the tectite version.
The tectite data sheet clearly states for potable water central heating and non potable water.
For use with push fit and press fittings.
We use them with press fittings as you need the longer stem.
Cast iron welding is tricky especially with this kind of thing which isn't likely to be high grade material. I think brazing rather than welding might be more successful. The best person would be an old school blacksmith type oif you can find one
All of the above cast is not easiest to weld ...
Round here they accept tube with soldered fittings on . Lots of paint gets knocked down to next level.
I weighed in yesterday heavy copper £7200 per tonne. braziery £6100 per tonne.
Mixed brass £3600 per tonne.
I can't say for certain on the JG controls but the equivalent Polypipe control has a built-in thermostat so the pump can't run until boiler flow reaches a pre set temperature.
So pump won't run constantly circulating cold water.
First suspect 3 port valve try switching of power to heating system and see if valve spring returns.
Honeywell have a really good smart phone wiring app which includes a fault finding guide.