Boiler water pressure drops from 1 bar to zero over 24hrs. Either the pressure relief valve is contaminated with debris or the valve is no longer effective. Service guide advises not to tamper with the valve. How can I clear debris from valve or ascertain if the valve has become weak and needs replacement?

John Fear, April 2018

Charge the system to 1 bar, then put a central heating demand on, turn the heating up to maximum and monitor the system pressure gauge as well as checking the relief valve safety pipe that leads to outside, look to see if it’s passing water.. if so, does the system pressure gauge on the boiler increase and keeps climbing? you’ll have to recharge the expansion vessel as well as clean/replace the pressure relief valve . Get a registered engineer to do this as working on the actual appliance is involved..

Snorky, April 2018