Hi, we have the above boiler for hot water and CH in our 2yr old apartment. The red "lockout" light has started to flash on the Aztec unit beside the boiler when it fires up. We are in an apartment block but our boiler is different (the last apt to be built). A neighbour said when her light flashed, she had to top up the water in the boiler. I haven't been shown how to do this, can anyone help me, I haven't a clue about these things. Thankyou Valerie