Fully-pumped vented system, Glowarm Fuelsaver MK II, Grundfoss pump, 4-litre pressure control sphere, HW indirect cylinder, Honeywell controls (Including 3 port motorised valve on boiler output) and Randall 24 hour electro-mechanical programmer. All equipment located in loft space. New-build installation 23 years ago.
With the central heating selected "Off" on the programmer, and HW on "Timed" radiators still hot. Turning down air thermostat to zero reduces radiator temperature to luke warm.
Is this just a motorised valve fault or M.V. + programmer error ?
I've already been up in the loft some months ago and used the valve manual slider to move the position - this seemed to do the trick for a while. Now the problem has returned.
Also, the system regularly vents water from the pressure release valve - it has done so from new. This occurs most frequently when the system is set to HW only. The pipe run from the boiler to the HW cylinder is very short, no more than a couple of metres.
Grateful for any advice.