yonika So… what’s going on there ?
It’s difficult to know….
- It could be that when the heat expands the metals, then the thread gets tight, especially if it’s stiff throughout the whole range, which eliminates the o rings
- If it’s stiff under pressure, it’s because again the thread will have a slight upward pressure applied.
- If it’s stiff after a shot, the sealed brew system gets up to about 12 bar, due to water expansion, this is relieved as doon as you lower the lever enough for the top group valve to open
So guessing a bit more, and I need to be careful here….especially as I don’t know the water used, whether you have descaled etc.. I emphasise, what follows is mostly guesswork
You got the machine and never saw my review of the valve itself which said the assembly comes (in my opinion) insufficiently lubricated and before fitting one should lubricate it. This was for the valve bought to fit on other machines. The logical corollary of this is, Lelit get the assembled valve, and fit it in the Bianca.
The second logical step is that if you buy a Bianca, it might be a good idea to remove the valve before using and add more lubrication.
The valve gets stiffer and you continue to use it…not worrying about it and not lubricating it. The O rings degenerate (they are EPDM, not FKM) and possibly some seepage of liquid gets in the threads. The pin thread is steel I think (guessing) and the nut is brass…steel and brass can react if surrounded by a little water.
Finally it’s so stiff you remove it and lubricate it, even replace the O rings, but the damage to the thread in the brass nut may already be done…you cannot buy the brass nut as a service part.
Under no pressure the thread might feel fine, but under pressure is when it gets hard to move due to wear, continual use simply wears it more until eventually it fails. Fortunately @Norvin may well have an effective repair for the nuts. It may well be worth people sending their nuts to him for his services, should he want to handle peoples nuts?
The article I linked you to gives you a link to a source of much longer lasting FKM (Viton) O rings £8 for 100 delivered.
P.S. I have mentioned the lack of lubrication I found on my one valve sent for evaluation and that I think they should get their supplier to change to FKM O rings. I may well contact Mauro to as the suppliers to make the nut available as a spare. I don’t know if that will solve the problem, but he might send me a few nuts to try?? They are owned by Breville now, so I am not sure if/how he can respond.