Thanks for that. Forum user @terryplumb very kindly offered to have a chat over the phone with me about her system. He's basically taught me how the system works and given me some good ideas to move forward with (Top bloke btw, many thanks Terry!).
I will ring the original guy back tomorrow and...
I’ve reset, pump is spinning but it’s only staying lit for 30 seconds then cuts out again. No hot water is even leaving the boiler anymore. Not sure why he’s added air valves. Mums clueless, she says he asked her what she wants him to do next and ring him after the weekend.
Yes it did, hence I left and told her to get it replaced. I’ve just got here again and he hasn’t replaced the 3 port valve, but he’s added 2 new air vents(?) on the pipe work to and from the boiler. I can’t even get the boiler to fire up now, the safety cut off kicks in so nothing even heats up...
Going to check for an air lock today but I'd have hoped that he would have checked that already. Tempted to sack him tbh, but he will still want paying for work he's done even though he hasn't sorted it. I think a second opinion is needed but it'll be pot luck who to choose.
He told me central heating works. I'm traveling down there again today to have a look at what he replaced. I cant answer you about whether it was a gradual loss of hot water over time but I will ask the question.
My mum rang me last week to say she was without hot water, so I popped over at the weekend to check it out. She has a WB Greenstar Ri boiler, and a 3 port valve running up to a vented cylinder. It seemed to me like the hot water was stuck in a loop sending it to the pump and back to the valve...