My boiler appears to cut out after first heating to the target temperature. once the max temp is reached it will ignite and cut out about every 5 seconds. Reseting appears to make no difference. However once the system has been allowed to cool to below 10degC approx it will function correctly again - until it reaches the max. CH seems to work ok although the rads only get warm during the "pulsing" never hot. I am happy it's not the exchangers as the system can generate hot water once the unit has been allowed to cool.
I'm sorry, it's not an answer but I have the exact same model with exactly the same symptoms! You described them better than I could. I gave up with it altogether yesterday and switched it off and used electric heaters in whichever room I was using. This morning (with snow on the ground) it appears to be working again so I had a quick shower before challenging it to heat the house. I'm concerned that if I call someone out it will appear to be working normally so they won't be able to fix it but will still have to charge a call out fee.
MJB
February 2009
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