How to repressurise strange boiler?

[Mottie]

I could yes, but I needed to use the Non-Return Valve that came with the loop, otherwise boiler water may have flowed back and contaminated my mains.

Very unlikely as your mains pressure would be higher than the system pressure. It has to be otherwise it wouldn’t pressurise the system. Did your shower head hose have a non-return valve? Only time the non return valve would do it’s job would be if your mains were switched off, you had released the pressure in your mains system and then there was a leak in the pressurised central heating system back into the mains system and that would only work if the flexi was still connected and both ends were open.

 

[SpaghettiCat]

Very unlikely as your mains pressure would be higher than the system pressure. It has to be otherwise it wouldn’t pressurise the system. Did your shower head hose have a non-return valve? Only time the non return valve would do it’s job would be if your mains were switched off, you had released the pressure in your mains system and then there was a leak in the pressurised central heating system back into the mains system and that would only work if the flexi was still connected and both ends were open.

Ah I see, good to know. I didn't know enough about that so took the warnings about contamination seriously.
The shower hose didn't have a non-return valve, so I connected it to the non-return valve that came with the filling loop.

The filling loop came with 2 valves on each side of the flexi hose: a non-return one and a regular on/off valve. I had to remove the regular valve so that the hose could be connected to the sink valve.