Vallaint ecoMAX 622/2 Boiler pressure low

[chassy]

Water pressure on Vallaint dropped to below 0.5 bar over last few days and then F.25 displayed. I noticed 2 rads in loft has a lot of air and had to bleed several times before water came out. Topped up several times yesterday but pressure dropped suddenly. Topped up again this morning to 2bar and pressure now hanging around 1bar (is that good?) for last few hours. Checked all rads, around the boiler and megaflow tank for leaks but dont see any. I did hear PRV drain water out of its pipe when boiler comes on so wonder if PRV faulty or could it be prob with Expansion vessel. How can i check b4 calling a plumber? Thx.

 

[chassy]

Any clues how to check cause of low pressure?

 

[aggis]

Expansion vessel has lost it's charge or the connecting tube to it is blocked, therefore when your heating is on the pressure guage goes over 3 bar & the prv blows off.
The Ex vessel hopefully can be recharged & you may require to change the prv, as often the it doesn't often seal after operating.