Drayton TVR4 radiator valves are very good and are trouble free for many years until they start to drip water, the best thing then is to change the gland seals without having to de-pressurise the central heating system saving time and expensive plumber fees. Had problems getting the gland seals initially but their customer services helped me to sort this issue. I contacted Screwfix who are looking at holding these seals in stock for customers to buy.