29-12-2011, 10:04 PM
Hi Mike,
Yes, that's my reading of the situation too. But, it is my belief - and I could of course be quite wrong about this - that a small bi-metallic thermal switch would be considered to have very low thermal inertia compared to the rest of the system. Certainly, just a section of 28mm copper pipe is pretty "hefty" compared to one of these switches - they are only about 12mm or so in diameter. Sure, an LM35 or equivalent probably responds faster, but what is "fast" in this context? I sense that the difference being discussed between these different sensors is seconds or perhaps 10s of seconds rather than minutes, and that this sort of time is probably short enough. Lawrence? I'm probably wrong - but interested nonetheless...
In my old boiler, one of these thermal switches was used as a safety cutout on the flow pipe - in a boiler with a rather pathetic and fragile aluminium heat exchanger. Another was used to cut out the boiler if the flue gas got too hot. A third detected the dry-fire condition. Not that anything found in this dreadful old thing is necessarily a recommendation in itself, but I've noted very similar things in the German replacement.
All the best,
Mark
Yes, that's my reading of the situation too. But, it is my belief - and I could of course be quite wrong about this - that a small bi-metallic thermal switch would be considered to have very low thermal inertia compared to the rest of the system. Certainly, just a section of 28mm copper pipe is pretty "hefty" compared to one of these switches - they are only about 12mm or so in diameter. Sure, an LM35 or equivalent probably responds faster, but what is "fast" in this context? I sense that the difference being discussed between these different sensors is seconds or perhaps 10s of seconds rather than minutes, and that this sort of time is probably short enough. Lawrence? I'm probably wrong - but interested nonetheless...
In my old boiler, one of these thermal switches was used as a safety cutout on the flow pipe - in a boiler with a rather pathetic and fragile aluminium heat exchanger. Another was used to cut out the boiler if the flue gas got too hot. A third detected the dry-fire condition. Not that anything found in this dreadful old thing is necessarily a recommendation in itself, but I've noted very similar things in the German replacement.
All the best,
Mark
