Why does my Glow Worm boiler start up every 90 Minutes?

12 Apr 2008
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United Kingdom
My Glow Worm combi boiler starts up approx. every 90 minutes for about 15 seconds. It sounds like the fan or poss the pump comes to life as it makes a whirring noise.

Is this normal, or is there a fault? Many thanks
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what boiler is it? if its a cxi, ultracom, or flexicom its a preheat function. perfectly normal.
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keeps the plate heat exchanger warm, so when you open a tap the hot water comes through quicker. It can be disabled.
On your hot water dial it has a dual function. From about 7oclock to 10 is min to max hw temp setting without preheat. Then from 10 to 5 is min to max with preheat. hope that makes sense, you should notice the difference on the markings around the dial.

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