Noisy Automatic bypass valve or pump

[Debsj1963]

Hi I have a vaillant ecotec plus condensing boiler which is in the kitchen with an indirect unvented centerstore cylinder in the airing cupboard. All has been well for 18 months (the cylinder was installed in April 2018.) The last few months there has been noise in the airing cupboard which sounds like a sort of whistling noise when the boiler shuts down and the pump speed starts to reduce (I believe this is the pump overrun). 4 engineers have tried to fix this problem by the first one turning down the pump speed (this took too long to heat the house and as we have microbore fittings restricted the water even further), the second increased the pump speed to it's original position but turned the Automatic Bypass Valve down, the third said it needed new AB valve which was duly changed. Still no joy so called the engineer again and he said that the ABV had been left fully open and so he turned it down. However shortly after he left and as the heating was going off the noise is still there. He said when he left he may have to change to a manual bypass. I am confused as to why this was ok for 18 months but now we are having problems. Any help would be appreciated as it looks like I have to recall the engineer

 

[MeldrewsMate]

If, I suspect, you have a zone valve for hot water generation, and another for heating then when the heating turns off (HW zone valve already shut) there will be a sudden increase in flow over the ABV, which will generate noise for as long as the pump continues to run (pump over-run). Turning down the pump speed, as you found out, helped with noise reduction, but not with heat distribution and, with microbore systems you need more motive force to shift the required amount of water through the pipes, so a reduction in ABV setting was not the answer either.
Some ABVs are noisier than others, some zone valves close more softly than others (so tend to cushion the peak dynamic pressure by holding open while the water's kinetic energy is dissipated).

Can you change the minimum pump run-on time in the boiler settings? It won't stop the noise, but may reduce its duration.

It may be that your solution lies with a change of pump to one with self-regulating variable speed, or with a change of brand of ABV, or by replacing a rotary shoe type zone valve for a Honeywell type (ball over orifice).

 

[Debsj1963]

Many thanks. I will look into changing over to a rotary valve.

 

[MeldrewsMate]

Many thanks. I will look into changing over to a rotary valve.

Please re-read my post....definitely not TO a rotary shoe type.

 

[Debsj1963]

Apologies I meant changing over from a rotary shoe type to a Honeywell type. Once again many thanks.