CH/HW Automatic bypass valve

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.

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.

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.