I had to replace the actuator head on our Drayton mid-position valve this week. I woke up last weekend to hear it oscilating. Helpful chap at Drayton suggested replacing HW cylinder thermostat as well, for the sake of a Â£10'er. So all done and we have now have HW and CH ok.
However, when the hot water is on by itself, the boiler (Glow-worm Ultimate 30-80FF) seems to start ok, along with the Grundfoss pump, but 2 minutes later, the boiler cuts out and the pump seems to continue. 3 minutes later, the boiler starts again and the process is repeated. The two pipes above the boiler are warm and the cylinder thermostat certainly trips the system on and off if rotated.
I'm a DIY enthusiast, but not an expert :?
Any ideas would be a great help. Thanks.