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

[woodbine]

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

 

[mickyg]

what boiler is it? if its a cxi, ultracom, or flexicom its a preheat function. perfectly normal.

 

[woodbine]

Thanks Mickyg. Its a 30 cxi.

What does preheat do?

 

[mickyg]

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.