Potterton Suprima 100 - lights with a bang (occasionally)

I have a Potterton Suprima 100. Occasionally (maybe once a month, could be more, could be less), it lights with a bang, burns really noislily for a few seconds, then shuts down. It usually then relights ok at that point (although once it did repeat the nosiy ignition/burning). Three engineers have so far not been able to come up with a solution. Does anyone have any ideas ?

Thanks

You have explosive ignition.

You need a competent gas engineer familiar with this model.

Try Heateam.

we had a couple of these the fault proved to be a leaking burner bar

Had another instance of explosive ignition this morning. Boiler started as usual, and then ran for perhaps 20 minutes. I then heard the gas valve close, and then a second or two later opened again, at which point there was the bang. There did not seem to be enough time for the shutdown/startup sequence to run properly. It then ran fine until shutdown by the thermostat.

My question is what could cause the boiler to stop and start again ? I don't think it was the external controls.

I do have someone looking at this, but it is so intermittent that any suggestions are welcome.

Thanks

Decided I'd had enough and got Heateam out today. New PCB assembly and a visit by Nationalgrid to replace the regulator. The whole startup sequence is a lot quieter. Fingers crossed we've nailed the fault, else they'll be back Monday.