I did, and replied there also ...
Its "safe" to operate even if it goes into the red - in the sense of that is what that valve is there to do, relive the pressure should it go to high - so nothing is likely to go pop.
have a drain points? The picture is a bit fizzy of that bit, but it looks like it has two sets of bits you could turn. One to operate the valve, and one perhaps is to drain on the boiler side of the valve?
I have to confess John I know little or nothing about combi boilers, so this is a whole new ball game for me, however before retirement I worked in the domestic electronics industry and wouldn't dream of involving myself in anything which is liable to be dangerous (e.g. tampering with the gas side of the unit) and although I'm knocking on a bit I'm still willing to learn from people such as yourself and others on this thread who have been kind enough to offer advice.
Unfortunately the service manual I have is pretty succinct in the way of explanation, which is fair enough as it's obviously aimed as a guide for professionals and not as a detailed instruction manual for a novice such as myself, if push does come to shove then my next step will be to start dismantling and check out the expansion vessel and if needs be order and fit a replacement.
The only problem that I can see will be the draining and re-commissioning, but as I mentioned previously, the unit is situated well above the hot water and radiator system, which leaves me wondering if it will make it an easier task to replace the EV, that is as long as you good people on here don't mind me asking you seemingly stupid questions if I get stuck :-)
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