I have an old Glowworm Fuelsaver 40B Mk2. Tried to fire it up after draining radiators to replace one in bathroom and cure leak in another. Also had a new bathroom installed. Bled rads so no air there. After firing up the main pipe above boiler gets VERY hot and starts to bang and shake violently. There is a \\\"Honewell\\\" box nearby and when held off auto, it stops banging for a while then starts again after a few mins after it moves back to auto.
Any ideas anyone?
Any ideas anyone?