vokera riello loosing pressure, how to figure out why?

forthetime

Well my boiler was loosing about 1 cm of pressure per day all last winter but my heating has been off ie the heating ie rads dont come on unless it gets below a certain temperature in the house and rads not been on since April and the boiler has stayed at exactly the same spot 1bar , until now (Sept) the heating has been back on for the last week and the boiler pressure has dropped to 0.5 bars!!
An engineer has checked the boiler over and can not find any fault with the boiler and no leaks from the boiler.

What could this indicate where the fault lyes?

missile

I had similar with my old Vokera. It was diagnosed as a leak in the diaphragm within the expansion vessel.

southcoastrgi

Could you clarify 1cm of pressure ?
You may have had some loss of water during the summer & turning the heating on may have caused the pressure to drop, 1/2 bar of pressure is next to no water really so I would top it upto 1.2 bar & see what happens, also check the rad valves for any weeps especially under the plastic caps if they are fitted

forthetime

I have since checked the tops of the rads which I didnt know you had to also do. The living room rad and the bedroom rad had water on and around the air bleed valves, not sure whats thats called but heres a pic of it. Could this be a leak? Could this be causing the boiler to lose pressure? How can I stop it leaking? ie turning it or tightening it? if so how? which parts? which direction? thanks all in advance.

could this be why the boiler is loosing pressure?

Is there a video on Youtube showing how to do this? What would I specifcally search for in the search button?

I have bought some tools to fix this, I bought:

Diall White PTFE tape (L)12m (W)12mm
Sentinel Leak sealer, 50ml
Magnusson 8" Adjustable Wrench
Magnusson S2 steel PZ0 Pozidriv Screwdriver (L)75mm
Magnusson S2 steel PZ0 Pozidriv Screwdriver (L)75mm
Magnusson S2 steel PZ2 Pozidriv Screwdriver (L)125mm
Rothenberger 10" Water pump pliers

Is that everything I need to do this? If anything else is needed toolwise, can you tell me what thanks again.

Its also leaking from the other nut without the air bleed facility.

Is there anyway to isolate those two rads so no water can leak from it anymore until it is repaired? Will simply turning it to Off rather than 1-5 stop the water leaking from the rads as the carpets getting very wet.

forthetime

Thanks, how do I turn off the towel rad in bathroom, I turned both those metalic things pic below clockwise fully but been leaking still.