theyre a twin pass heat exchanger so maybe it is overheating when they are both used. example, gas to water exchanger has a route for heating system water and a route for cold mains to pass through to be heated by the flame,
just a thought but maybe when the heating sys is not being used so much and that heating sys is cooler then it may be managing to get rid of its heat through the cooler water and when the heating is being used its struggling as it has less water to keep it cool.
it may only be a couple degrees thats pushing it just over the edge to the point the safety t/stat (on htg pipe) trips and since its inline with t/couple you get the click and pilot out. it is a awkward one as the easiest repairs are when something is plain and simply....fooked.
scale/sludged system stopping heat from dispersing quick enough.
This isnt a boiler ive personally worked on much so hopefully someone might have a better idea for you, the only experience ive had lately is ive just ripped one out today and swapped for a nice new baxi, and i kept the main exchanger for scrap/lager fund :-)
without getting hold of a manual i cant say for def what the boiler incorporates but i would hope gas pressures have been checked and any main temperature sensors
Hope you get it sorted and what a good post, all details, thoughts on patterns etc wish many others would follow suit.
ste
December 2009
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