Boiler Thermistor general enquiry

2 May 2010
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United Kingdom
Just a quick question if anyone knows the answer to this: new boiler suse thermistors now instead of thermostats. So how do these work? I know they give off resistances at different temperatures, but is there a range? What I mean is, on the older type boiler the thermostat would break at a set temperature and then make again when the water retruned cooler, and this would cycle on and off.

But how do the thermistors work? Do they break at a certain temperature to?
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The resitance changes with temperature, the burner control PCB interprets the resistance to calculate the actual temperature, and modulates the gas rate down to low fire and eventually off, this modulating type of control is much more energy efficient than ON/OFF control. ;)
I see, so the pcb itself stops the boiler from firing when the thermistor is at temp (or should i say asjusts it to low gas)

If when testing a thermistor, you get inifinty reading this would mean it was faulty?
(boiler wouldn't fire)

Same if it were stuck closed (no continuity) - temp would get too high/boiler lockout?

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