The Efficient Home Forum

Due to not staying at my place for extended periods and the weather as cold as it has been for many years, I have left the controller on the “Away” setting, which sets all rads at 12C. Not too hot, and nicely aired I thought, but I noticed that the CH valve switches off, then a few seconds later switches back on again, then there’s a delay and the same thing happens. I know it depends on which valve is calling for heat, but it does strike me that I am going to get a premature failure of the V4043H don’t you think?

How is your system setup? Page 43 of the evohome installation guide shows a 'figure 4' diagram and this was how evohome was designed to work with TPI systems. It is done slightly differently on OpenTherm systems with a new scematic we call 'X Plan'...

TPI'ing of a zone valve when not necessary will eventually lead to failure, but this practice has been going on many years with TPI thermostats, not just evohome.

Thanks for that Richard...when Ime near the manual next I will have a read.
On a related subject, in a past life I used to maintain industrial temperature (and flow, and pressure) controllers which used full 3 term control....proportional, integral and additionally derivative. Derivative was a control function which was used on long lag systems with the potential for significant overshoot. It looked at the rate of change of the measured value and even if the measured value was below the setpoint it wound down the controller to eliminate overshoot, working against the integral control action which still saw the error between measured value and setpoint winding the controller up!
The problem with Evohome of course is that the control action is dependent on the number of different zones, the industrial example I gave was only one zone!