My toilet cistern takes 15 minutes to fill after a flush, do I need to replace the filler valve, and how do I know what size thread to it is?

Hi Effy

Depending on the age of the fill valve you could try cleaning the fill valve washer of sediment. If that doesn't work then replacement is the only other reasonable option. Check out this video for a basic fill valve repair:

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If that doesn't work out and replacement is needed you need to get a replacement that works for your toilet so bring the old fill valve with you in a plastic bag when you go shopping (or take picture of existing one and take it down to home inprovment store or plumbing supply store).

Back to you

Mark

Hi effy and welcome to The Plumbing Page at AMHD.com. You must first deter if you have pressure to the fill valve. Shut the water off at the angle stop and Remove the supply tube. Now p[lace a pan over the top of the stop and one underneath to catch the splash. If you have a strong stream then replace the fill valve of your choice. Any one will fit. If the stream's weak then get back and tell me. Good luck, Tom