The reliable way to hire a tradesperson

Fairly new oven, trips out when warm, think it's got to be thermostat anyone can help please

hi, we've been having issues with our architect and are thinking we might be better taking on stage 5 riba without them. we are doing a ground floor extension with some changes to internal walls/bathrooms. we have gotten to the stage where we have tender documents now and have been trying to understand the regulations on line with respect to getting sign off from a principle designer as part of building completion. some sites say that an experienced builder can provide this, others say that it needs to be someone specifically qualified. im not really sure if we end up parting way with this architect if we will end up needing to pay out for a new architect to take over and provide that sign off. also, i'm not sure if the expectation would be that the building company could/should continue conversations with structural engineer/building control/party wall surveyor or if we'd have to do that. sorry if the questions are a bit haphazard or dont make sense! new to this all. i'm also not sure if i'm thinking about/asking the right questions or if there are other things i should also be asking or considering! thank you very much for any advice and suggestions in advance!

Kitchen sink is blocked. When washing machine turned on the water comes out the kitchen sink