I have a Baxi Bermuda back boiler (the type with a gas fire on the front). I turned off the gas supply to the house when we went on holiday and now I can't get the pilot light to come on. I press the big grey button almost in line with the pilot light (at the front of the controls) and at the same time repeatedly press the small ignition button on the gas valve. I can see a spark but there's no ignition. Am I doing something wrong? I can smell gas when I've done this a few times (yes, I do then wait for a while before trying again!) so I know there's gas getting to the boiler. Any suggestions before I call an engineer?