Leaking filler loop valve on Vaillant Ecotec plus 831 boiler

Hi there, I'm new to this forum and was hoping someone could help me solve a problem on my Vaillant Ecotec plus 831 boiler at home. I have 5 years experience as a pipe fitter and NVQ l2 in plumbing but never touched a boiler before so a bit green in this area.

I fixed a leak on a 10mm jg manifold on the heating in my new house a few weeks ago, a day or so later, I noticed the pressure gauge on the boiler went well past the 1.2 bar I set it at after refilling and bleeding the rads and into the red. I drained some water out of the system and it happened again. The previous owner had left the filling loop on so I disconnected this and realised the grey handled valve on both sides was letting-by water into the system and raising the pressure. Just wanted to check if there could be an underlying problem that has caused this valve to malfunction? Also is there a way to fix it or would i just need to swap the part? I have left the filing loop off and am letting it drip into a bowl for now. Also now noticed that the diverter valve is leaking when a hot tap is run and have ordered a new one as I have read that they cannot be repaired once they start to leak. Could the diverter have become damaged when the pressure was in the red on the gauge or otherwise be associated with the dripping filler loop valve?

Any advice appreciated
Thanks

Take the grey handles off and check that the brass nibs are fully off, the handles round off.

Thanks for the reply. Took them off and tried a shifter on it. Wouldn't want to go any harder for fear of snapping it and its still dripping just as much.

If I also need to replace these valves should i just get vaillant to replace the DV as well for £300 as I just read on a different thread?

Seen this before on ecoTEC, just another example of poor quality from Vaillant.

The £300 you refer to is a one fix one fee. You have two 'fixes' by the sound of it.

Thanks simond. I think I have three...The valve on the boiler side is also letting by but at a slower drip rate!! Is there a reason you know of as to why these 3 valves have failed around the same time? Do you know what these valves are called so i can look for some prices of these fittings?

The £299 is a fix up to 3 parts get them to do it

My two year old ecotec 824 plus had/has exactly the same problem. The design of the built in filling loop is useless - there's a thin braided hose like standard filling loops, except thinner with odd sized threads on the ends and no easy way to remove it. The valves only need the very slightest leak to mean the pressure will creep up until cold boiler pressure equals mains pressure ( 5 to 6 bar for me)

I have disconnected mine - one end is capped off with a screw cap from a standard filling loop kit and at the other end I think I've got a second double check valve body (can't remember without going and looking at it). Longer term I plan to completely remove it (and use interchangeable parts without the filling loop nonsense from the more basic models) and fit a standard external loop where the hose can be removed and the ends capped - as it's supposed to be to comply with the water bylaws.