honeywell 3 port valve buzzing

[hardtail]

hi lads my 3 port valve on my y plan has started humming ,its about 5 months old now,it seems to start after the heating has been on an the only way to stop it is to switch the isoiation switch off ,it seems like when i turn the power off the valve resets itself if that makes any sence any ideas

 

[Meldrew's mate]

An anomaly in the design of this and most other 3-port valves is that the valve stays at the CH position at the end of the heating period (usually because the HW is hot by then), and stays there until the next call for hot water - possibly the next morning. The buzzing is the synchronous motor in the stalled position.

You can test this by turning off the mains for a few seconds after the heating timer has gone off, the valve will return to its "relaxed" state and be quiet. It will stay there untill the next demand for CH. Alternatively you can turn the HW demand on for a few seconds after the CH has gone off, with the same result.

There is another possibility, though a much rarer one - water in the electrical part of the valve, though not normal in a 4 months old one, and that is more of a "fizzing" noise just before the RCD trips or the fuse blows!!!

MM