Boiler stops heating water occasionally


Hi,
I have a Glow-worm condensing combi boiler (can't remember the exact model number), and recently it has decided to stop heating water occasionally. For example, you switch the shower on (it is a shower connected to the boiler and not an electric one!) and leave it running for a few minutes. After the first couple of minutes, the water goes stone cold for about a minute and then starts heating up again. The cycle seems to repeat itself as well.
I've tried using the taps instead of the shower and the problem is still the same.
Any suggestions would be appreciated.
Thanks.
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On 26 May, 13:17, snipped-for-privacy@hotmail.co.uk wrote:

This is probably due to the secondary heat exchanger being furred up, this is used to heat the water, so the system overheats and then turns off until the overheat thermostat resets. This can be cured by replacing the secondary heat exchanger it possible descaling it.. I have used fernox heating descaler on mine with success.
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This can be cured by

Used brick acid on mine ... bit nastier to use but it works a lot quicker
Ash
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