Boiler on cold rads but hot water?

Hi PLEASE HELP!
Had a ravenheat csi 120 lox nox installed three years ago. Had Ravenheat out 9 times within 6 months. All has since been fine, however now the rads have just stopped heating. We had the electrics of due to electrical work being carried out on the house. The temp was about 4celisus. Once the power was back on all was fine, then later the rads just stopped. The water is fine light is on the boiler, the light for the heating is not on.
Boiler in a cold garage, the Corgi chap turned up had a 5 min look and said the pipes are not insulated and this has led to the boiler freezing?!! I said when we had temps of -15C all was fine.
Even though the light for rads is off, advised I heat the pipes with a hair dryer..........is this cac? Or the an actual remedy to the problem.????? Thanks in anticipation.