noisy boiler when switched off

[gorgonite]

We have a wallmounted boiler (Glow Worm I think), and the system is one that uses a hot water tank. System is approx 15 years old and is in a 3 bed bungalow with a Grundfos pump in the loft.

The system heats water and rads fine. However when switched off the boiler gurgles and burps for about 10 seconds. At night we could always hear the boiler humming through the house, but now it seems a little louder and the humming is rough not smooth! (Hope this makes sense). Is this a serious problem, and is it better to replace the boiler. I was told by an engineer that the heat exchanger usually packs in around this time and it's more cost effective to get a new boiler?

[kevplumb]

first what make and model ??

"i think" ain't a lot of use

[gorgonite]

It's a GlowWorm EnergySaver wallmounted