Boiler 'cutting out'

I have a Barlo Balmoral boiler (not a combi, the other sort!), not made anymore, but spares are available from a company called Halstead I believe. The boiler has started cutting-out recenlty, ie it will be burning away happily and then just cut-out for a second and then relight. It does this quite frequently throughout the day. I had a bolier man come round and have a look, and he recommended I have the pressure switch replaced (fair enuff I thought). Well it doesn't seem to have made a lot of difference after he did this, so I've txted him but in the meantime wonder whether there are any gas engineers here who may know this boiler or may just have experience of this type of problem and know what to try next, in case my boiler man doesn't know what to try next? TIA tim
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