E10 light flashing on Remeha Avanta 18v boiler?

It says check the water level and check for leaks, also check wiring between heat exchanger fuse and the vent system.Check the pump and open the radiator valves.
Contacted Homserve as we pay lots to cover in case of problems but they are CRAP which is a polite way of putting it.
DO NOT TOUCH N POWER OR HOMESERVE THEY WILL LET YOU DOWN.
MY QUESTION IS HOW DO YOU STOP YOUR PIPES AND BOILER FREEZING UP UNTIL ENGINEER COMES OUT

Neil Evans
December 2014