I've now run out of ideas to solve my Glowworm 60B Balanced flue from cutting out.
1.pump works ok
2.motorised valve and thermostat on HW ok.
3.motorised valve and Room stat on CH ok.
4.HW works ok
5.CH comes on for 30secs then turns off for 5 mins.
6.Removed supositary shaped boiler...