My E180 woodgun has a Riello oil burner built into it. We use oil to heat domestic water in summer, recently the burner will fire for about 5 minutes then flame goes out, if I push reset it will fire again and burn for another 5 minutes or so and I have to keep doing this to get water up to temp (170). I put new oil filter and nozzle in a couple of months ago. Anything else I should check or change? Thanks