The bath tap in our house is old (~40yrs). The valve which diverts the flow into a simple shower fitting no longer works. The whole thing should screw out but the threads are locked solid. Here is a picture of the bit
TIA Frank
Angle grinder.
Get it really hot with a blow lamp & try then.
It often helps alternately to tighten and slacken (until the nut gives).
One of the best tools on a rounded nut is a mole wrench. Set the adjustment screw so that you can only just close the jaws with the nut in the rounded section. The serrations will bite into the nut and shouldn't slip. HOWEVER you may have threads here which are seized up with limescale, in which case it may not be unscrewable short of removing the whole tap and soaking in hydrochloric acid for a long time.
Rake around the periphery of the joint between chrome disc and tap with the point of a stanley knife, taking care not to scratch it. Try and shift any crud out of the gap that has accumulated.
Soaking in a mild acid may also help break down any scale that is holding it solid.
Hot cold cycles, or tapping with a hammer may also help. In the worst case using an old screw driver and a hammer to drive the edge of the disc round - but that will damage the appearance, but you can do it close to the back where it won't be so obvious.
Yep.
If the thread is about the same size as the disc then that small square (IIRC) "nut" on the shaft isn't going to break a well crudded up thread that large.
But surely the shaft is the pully/pushy diverter for the shower so wouldn't be attached to the disc? I suspect the the disc is just a cover for the main nut for the diverter valve underneath. The knob will have to come off to allow the disc off and socket onto the revealed nut.
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