water runs cold after a minute or so

This a common problem with combi boilers, if someone is using the shower you need to make sure no one else is using water as yhe boiler struggles tonsupply water to more than one tap at a time. The other fix would be to have an electric shower installed, then would then heat the water.

This a common problem with combi boilers, if someone is using the shower you need to make sure no one else is using water as yhe boiler struggles tonsupply water to more than one tap at a time. The other fix would be to have an electric shower installed, then would then heat the water. Make sure the boiler is serviced annually

I am not an expert on this topic but it does sound like a similar problem we had many years ago. When you turn on a hot tap, water passes into the boiler via a diaphragm which tells the boiler to fire up and heat the water flowing through. Our boilers diaphragm had a tear in it which meant the boiler was struggling to get the signal to fire up and heat the water. Wether this is the case or not your first contact should be a boiler engineer who should be able to diagnose and solve. I doubt if the problem is related to pressure etc if it’s a new problem and nothing else has changed.

This could be a fault with the diverter valve in the boiler I would suggest having the boiler serviced