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From: Cynic on 26 Apr 2010 07:16 On Sun, 25 Apr 2010 11:21:43 +0100, "Mortimer" <me(a)privacy.net> wrote: >I wondered whether it was the "burner lit" sensor (is this still a >bimetallic strip?) I'm by no means a boiler expert, but the only two modern gas devices (a boiler and a room heater) I have had reason to look at both used an ionic sensor for the pilot light. Such a sensor uses the fact that the air inside a gas flame contains ionised carbon atoms. A wire positioned to be inside the pilot light flame when it is lit has an electrostatic voltage applied to it, and an electronic circuit senses when that voltage produces a current flow through the flame. As there are no moving parts or contacts it *should* be more reliable than a heat sensor as well as being faster acting. The room heater had the sense wire very carefully positioned so that a small decrease in the size of the pilot flame would take it out of the conductive area and shut down the heater. Apparently (I was told) the flame size and shape changes if there is an excessive amount of CO or CO2 in the air feeding it, and so this is a safety feature that will shut down a heater that is operated in a room with inadequate ventillation. I have no idea whether a boiler is set up in a similar way. All the above information was gathered from unverified sources, so I cannot vouch for its accuracy. -- Cynic |