hey,
my powermax 155 is doing the exact same thing, in fact its just gone to lock out as i.m typing this! and i cant fire it up again...its the 4th time tonight and its bloody snowing!
ive had 2 engineers out and they were both baffeled to what the promblem is...neither the less they still charged me to look at it and scratch their chins! so ive give up...most people wont touch them! i'm affaid the only option is a new boiler..or you could try turning the gas off and taking a large hammer to it! it wont fix it but it will make you feel alot better!!!!