Bath hot tap water flow slowing.

The tap washer could be knackered or the jumper that holds the washer might not be rising up from the seat as it should. As far as I know, a water softener will not remove existing limescale, only reduce formation in the future.

AIUI, the softened water does dissolve the deposited limescale and _gradually_ (where gradually means "a long time') ... the result, of course, is to get new-hard-water from the softened water taps.

Over a long period, yes.

You could also tip a load of descaler into the water tank

..but dont drink from any taps till its run through..

No tank, I have a combi!

Descaler is usually acidic. If the OP has copper water pipes there could be problems, if I remember correctly from my chemistry lessons, due to copper reacting with an acid. A plastic tank should be OK, but galvanised steel might be a problem.

Ah..all you can do is shut the water off, take the tap apart and try and descale it..

Softened water does, over a longish period, remove pipe scale.

Oh, indeed. Descaler etches copper and scars chrome. BUT it attacks scale about 100 times faster..so in general you do it once, and then fit a softener..

Now that info changes the game quite a bit.

The slowdown is probably in the boiler. The other taps probably don't show the slow down as badly as the larger bath taps. To accurately diagnose the problem you will need to measure the flow rate at the taps and really see if the bath tap is much worse.

I'd agree about the jumper - there is a circlip that sometimes comes adrift. Easiest thing is to change the enitre assembly.

A softner will remove existing limescale - in about the same time as it took to build up in the first place.

You were about to say something?

If it turns out to be that the problem with the hot water flow slowing down is within the boiler, what is likely to be the problem?

Steve...

CaCO3