7 year old boiler, noticed code 21 (radiator circuit pressure low) so she opened the filling loop but left it open too long. It auto-vented, but kept going until the red light came on and code 21 again, in minutes.

Every time hot water is needed, pressurise it up to about 2.0 bar, then it will run happily until it depressurises.

(Since the water supply doesn't depend on the radiator circuit being full, why does the whole thing shut down??)

Suggestion (from a gas engineer pal) is the 3 bar valve has stuck open, which I am confident I can replace, but I would be grateful for any other opinions and/or advice.

Many thanks

Rob Green, June 2013

is water constantly running from the pressure relief at the outside of your property? if so, a new p.r valve is needed. the pressure on the gauge when working correctly, should be, between 1.0 - 1.5, otherwise the boiler might go to reset if it isn't.

dave e, June 2013