Got summoned by SWMBO to investigate the case of the gas oven not fulfilling its number one purpose for being...
Symptoms seem to be:
It had preheated and was running ok. Set to gas mark 8 it had been on for 20 - 30 mins when the igniter started sparking intermittently. The rate of ignition attempts increased until almost constant. At this point she turned it off and called me. I relit it, and it went into pre-heat ok, and appeared to be working normally again[1]. However, shortly after it resumed the previous behaviour. SWMBO also reported a smell of unburnt gas which would suggest a genuine flame failure. She found that if it was turned down to gas mark 6, then it stopped attempting to ignite, but going back to mark 8 caused a resumption of the problem.
So, likely causes? What to investigate next?
Oven is in a Parkinson Cowan "slot in" cooker. Approx 14 years old.
[1] Although I did not actually test the gas pressure at the time, I did verify that there was no apparent drop in flame height when the boiler kicked in for HW production (35kW).