Boiler on the blink!

Arriving in from work this morning the house was freezing cold! It was a shock to the system as it was such a cold morning with snow on the ground. It seemed it had entirely lost the pressure & we hadn't needed to charge it up since it had been installed in July. Recharging it wasn't clear & so after googling & checking the instructions we phoned the engineer who installed it. He popped round within half an hour & showed us how it was done, easy when you know how. We were so grateful to him! He thinks a large air pocket had formed after two radiators were changed when the kitchen was installed.
Please excuse the phone shot, I have a software problem with my laptop at the minute.