CH/HW Automatic bypass valve

[AlanC]

We have just converted from vented HW to unvented. The change also involved switching from Y plan to S plan with an automatic bypass valve. The previous Y plan setup just used the bathroom rad as the bypass mechanism. We have noticed a fairly loud squeak. I have managed to track it down to the auto bypass value. When the HW (or Heating) is satisfied and the shutoff valve closes, the pump will continue (overrun) which causes the pressure to build and the auto bypass valve to open - all normal stuff. I was just wondering it is normal for them to give out a loud squeal when they open. Are some better (quieter) than others? Thanks Alan

[Roger Mills]

I've got one in both of my properties, and have never experienced anything like that.

They don't work very well though with intelligent pumps which reduce the speed when the flow resistance increases - 'cos there's then not enough pressure to open the by-pass.

[SteveW]

At some point I will fit such a pump, having already re-sized radiators and piping to drop the boiler temperature to 60°C (I may be able to go lower, but I'm waiting for colder weather to experiment).

However, rather than thermostatic valves, I have a timer/thermostat and motorised valve per room.

The plan is to replace the automatic bypass valve with a normally open valve, closing it when any of the other valves is open and letting the boiler control the pump overrun.

[Davidm]

Re that last para I'm considering doing just that, as I'm not convinced that my Honeywell auto bypass valve (a new replacement) is working at all. The water pipe on the downside of that valve seem always hot after the whole system has warmed up, but that may just be due to heat conduction along the pipes. The bypass loop is very short, 20 inches maybe, before it joins the main return to the boiler. I think that the nornally open valve could just be controlled by the boiler demand signal from the wiring box/centre, so that when there is demand for heat the valve is driven closed.