My Ferroli Modena 80 is discharging water through the discharge pipe each time the boiler shuts down. The pressure drops to zero and if I refil the system then it will work perfectly until the next shut down. I have a contract with British Gas but they will not attend until 7th January because I am not without heating!!! Is there anything I can do the rectify the problem?

David Beattie, December 2009