My boiler keeps loosing pressure, I have taken all my floors up to check for leaks but can not find anything.

Check the pressure relief valve ,is the pressure going very high when hot?if so no pressure in the expansion vessel

Hi, Check all the radiator valves and connections. Even the minutest leak from these will cause a loss in pressure over time. If these are all ok there are a couple of other avenues. Firstly the boiler itself has a pressure release valve which is usually set at 3 bar and the water outlet usually goes out directly through the wall behind the boiler to the outside. The 15mm copper pipe is quite easy to spot as it usually is L shaped with the outlet pointing towards the ground. If there are drips coming from it that could be your problem. Maybe some sand in the seal is causing a leak or the seal itself is damaged and the valve will need replacing. The other possibility is that if your boiler has a pressure regulating tank in it, the pressure, which is usually set to 1 bar, is down and water is being sucked into the tank which will affect the boiler system pressure. Both these last two ideas, whilst not being mind bogglingly complicated, really need somebody who knows what they are doing to have a look. Regards, Guy.

you dont have a leak. you have a faulty part. It could be one of many things, prv, heatexchanger; post job and ask for a Gas Safe engineer to come and repair your boiler. Ask to see his ID card before you let him/her into your house.