baxi duotec combi 24he boiler, loud high pitched humming, whining noise.

10 Nov 2015
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United Kingdom
I have an 8yo old baxi duotec combi 24he boiler.
When the gas central heating is running, it makes a constant loud high pitched humming/whinning noise.
The tone lowers for about 5 seconds, each time the boiler reignites to heat the radiator water. Before then returning to the same level.

I am in the room above the boiler, the noise is quite loud and its persistence gives me ringing ears.
[see the link to hear the noise, recorded upstairs. the recording does not capture how loud the note is, only its tone ].

Further info,
If the central heating is off, but the hot water tap is turned on. The boiler makes the same sound but at a much quieter level.

the diverter valve?* was replaced last week, but the noise is still there.
*Im sure the engineer said he replaced the diverter valve, after I also said that when the hot water tap is turned on for over five minutes, the radiators would fill with warm water.

My questions:
1. What is the noise likely to be coming from in the boiler? [or where has similar noise come from in other related boilers]
2. And when I call out the baxi engineer again, to attempt to identify the noise source. What are the likely parts, where they should first start their fault finding?

Last edited:
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