Honeywell 3-way valve buzzing while boiler is off

16 Apr 2020
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United Kingdom
Hello everyone,

The Honeywell V4073A1039 valve in my airing cupboard started making a buzzing noise late at night and early in the morning about 2 months ago. I bought and fitted a replacement Syncron motor a month ago but the valve started buzzing again last night.

It's a sealed system, about 3 years old and is controlled by a Honeywell ST9400C programmer.

The programmer has both the hot water and heating set to auto.

The buzzing happens occasionally, late in the evening and early in the morning, when the boiler is off. Does the buzzing mean that the valve motor is being energised? Why would it be doing this when the boiler is off and there is no demand?

Can anyone explain why it's buzzing and how to stop it please?
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It's inherent in the valve design - if the heating goes off with the valve at heating only, then the valve will stay there due to the HW OFF wire being live when neither heating or hot water is required.

Buzzing suggests something is loose or worn, and is an unrelated problem.

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