We have a vaillant ecoTec plus combi boiler - for a while now the pressure has been steadily increasing, we release the pressure by draining some water from a radiator, and then it creeps up again. The heating is not being used, so the boiler is only switching on for hot water. We have had an engineer out twice and he seems stumped, but has suggested replacing the expansion vessel, however from what I've read the expansion vessel would only cause the pressure to increase if the heating is on, is this correct? I'd appreciate any help!
Thank you,
Laura
