The boiler keeps shunting water out thro' the pressure release vent, although the pressure is showing under 3 bar. When pressure falls to '0' , boiler keeps working, but eventually fault No.'04' shows & the boiler shuts off. When filled, water is again shunted out, about 1/2 ltr., (I catch it in a plastic bottle) then steadies to a slight drip. Is the pressure gauge faulty?

Raym, January 2010

If the pressure in the boiler goes above 3bar the pressure safety valve will open to release some water to reduce the pressure. Unfortunately the valve never reseats itself properly usually due to sediment and will leak constantly. it needs to be replaced. A little difficult to get at but easy to change. The more important question is why did your pressure go over 3 bar? unless someone overfilled your system the problem usually lies with the expansion vessel. This is an air filled balloon located at the rear of your boiler which compensates for pressure rises in the system. If the air has leaked out the system cannot deal with the rise in pressure due to for instance the heating being turned on. You then get the sequence of events you describe above.

Synthesi 29e veteran, July 2011

Your pressure relief valve is faulty. cost of part about £13.

terry gas engineer, January 2010