Thank you all! It’s a Surrey flange taking water from the top of the hot water cylinder. This wasn’t fitted at first but the plumber came back after the problems and fitted it then.
Apologies - I’m not sure what the difference is between the supply coming from the HW cylinder or HW pipe work...
We have a very nice plumber who has redesigned and fitted the bathroom so we are not DIY-ing as such but I would really appreciate some advice.
Our plumbing is gravity-fed with a cold water tank in the loft and hot water cylinder (vented) in the airing cupboard. The plumber fitted an Aqualisa...