Boiler not running after system refill

Hi! During decorating a leak occurred in a pipe to a radiator. A plumber attended, drained the system, fixed the leak and refilled the system. Now, however, the boiler (an ageing Stelrad Ideal Classic RS model) won't run for more than a few seconds before cutting out. The instruction sheet I have mentions a reset button, but this is not present on the boiler I have. Any help appreciated, as I have two small children, no heating and no hot water

There is a manually resetable overheat stat. pull down the plastic flap front bottom, look inside to right of what is behind that, between side of boiler and metal box which houses control board is a red cross shaped button. Push this in.

Maybe the boiler has air trapped inside it and is overheating, this needs addressing.

Thanks for the reply Paul. Looked inside as you suggested, but the red cross shaped button is not there. I suspect the boiler is an older model (leaflet with it dated 1990), the leaflet does mention a reset switch for sealed systems, but there is no switch in the position indicated. I suspect that you're correct in saying there may be air trapped in the boiler. Not something that I could fix? Thanks again