Fed up. After wasting all afternoon on this, my boiler now fires when the cold taps are turned on. Doesn't heat the water, it just fires up as if it thinks it needs to heat water, then goes off again. Never did that before. So I try to fix one thing and 3 more problems arise, it's like dealing with a fucking Hydra. I've fucking had enough. My life is nothing but firefighting and not sleeping, 24/7. Fucking pointless, I can feel the damage all this stress is doing to my body and there is no way to stop it, because stopping just causes financial collapse so I'm completely trapped 😢
ETA: I think I fixed the fucking issue, I had to go around running every tap in the house to rebalance the water pressure, now finally seem to be able to run the cold water without the boiler coming on 🤷