whistling baxi combi instant 105he

29 Jan 2008
Reaction score
United Kingdom
In last month, boiler has started whistling after using hot water. Run water, switch taps off, then get whistling while pump does its overrun. Gets quite loud but is unpredictable - sometimes whistles sometimes doesn't. Started happening after replaced dhw pressure differential valve diaphragm, but maybe that's coincidence.

Seem to remember posts a while back about o-rings in diverter valve - does that sound right?

If it is the o-rings, can anyone tell me where exactly they are and how to replace? Thanks
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It's probably the fan bearings wearing.
My boiler does the same. The fan makes all manner of noises when it slows down. It needs replacing but I can't be bothered. Selling the place soon.
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your quite right with your own diagnosis. If you have the manual for the boiler look at the section for replacing the plate heat exchanger.
id start there first as its a cheap repair and most likely.

Definitely sounds like the diverter valve. My boiler does it too.
I have proved this by removing the actuator head and wiggling the diverter pin. I can change the pitch of the whistling, and make it stop all together by doing this.
Thanks Ray and Gareth. Plate heat exchanger was replaced last year so reckon should be OK. Will try Gareth's suggestion and see what happens.

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