I too have installed a couple of these and get flashing OPTIMUM and STOP late in the evening maybe 30 minutes before the heating is due to be off. No doubt I get the same in the morning for OPTIMUM START but I'm not up early enough to see it! I agree the instructions are a bit vague, but suspect...
replaced venturi but boiler still only firing with case off. replaced fan assembly and all was well - for a day. Then the boiler fires up, runs for 10 mins then goes off but pump does not continue (no pump overrun) and the green demand light is not on - ie it doesn't flash green. After cooling...
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