It's all sorted now, but.....
Our side/back door, jammed recently. The multipoint locking system, was failing to fully retract, when the handle was lited, just around a 3mm gap between door face and frame. It would close, and lock with the key, just fine - just couldn't open it.
A bit of research, suggested, ragging the handle up and down fast, to try to get the multipoint released. In fact that worked, after which the multipoint with door open, seemed to be retracting normally. It worked just the once, but at a time when the door needed to be relocked, I had to rush out to an appointment.
Back home, I tried the ragging the handle up and down again, whilst both pulling and pushing on the door, but all I could manage, was a partial retraction of the arms. Next day I tried hammer on the door, jacking the lock side up and down, nothing helped - still jammed, three days later.
I finally conceeded defeat, and tried to find an honest locksmith, emailing a few, explaining the problem, for a quote - I'm still waiting four days later, for a reply from them. Then I remembered a mention long ago, that a local cobbler, knew a bit about locks, so I popped round an enquired. He agreed to take a look. He arrived, spotted that the handle had been slipped on temporarily, pointing the wrong way, and asked me to go through the house, and adjust it.
I set off, but by the time I had made my way to the back door, it was already open. I heard no noise, I saw no tools, yet he'd managed to release the door, like magic. He made no charge, but what did he do?
It was obvious what the problem was, the gearbox was broken and not operating the multipoint rack properly.
Whilst it was open, I removed the entire lock, and multipoint rack out, wedging the door shut with timber, until I could organise a replacement gearbox.