Just in case everybody was worried that I might have been launched into outer space by the explosive ignition, I shall put your minds at rest. The saga continues but just possibly may becoming to some sort of conclusion.
Since the last posting, the 2 foot of 15mm pipe has been replaced with 22mm. There is now only 2 inches of 15mm into the boiler. This may have made a slight difference, but did not cure the problem. Next the burner was changed. Absolutely no difference. Then I had a suggestion from another newsgroup that fluctuations in the mains voltage could have an effect on the flame detection circuit. The mains voltage does indeed vary between about 233V to 241V, but could not really detect any pattern between volts and explosive ignition.
So now I conclude that the only way explosive ignition can occur is that unburnt gas has got into the flue before enough gas has passed over the sparking electrodes. A previous posting describes the mechanical construction of this boiler, and how I thought this was possible. Fortunately this construction provides for some simple experimentation. I have now placed a carefully hand crafted piece of right angled pipe under the burner to deflect some of the incoming air/gas mixture to the other side of the burner (where the electrodes are). The effect so far has been dramatic. To date I have had no explosive ignition. A few more weeks are required to confirm. And what's more, the consistency of the ignition has now improved. Whereas before, even when the ignition was not explosive, the loudness of the resulting pop would vary from virtually nothing to something of concern. But now I can hardly hear the ignition at all. I daresay that in a couple of weeks, I shall be proved wrong, but so far the results are very encouraging and could prove that the Suprima 120L either has a design fault or requires such careful setting up that it is more by luck than good judgement it works correctly.
I am now waiting for the thought police to come and take me away.
