bath mixer stuck bonnet

[plomero]

One of the cassettes/valves in my bath mixer tap has gone, so I'm trying to get it out. I can remove the handle but am unable to unscrew the bonnet (see photo). I'm using grips but it's not made any easier by it being a sloping surface. I've tried spraying WD-40 and descaler around the base and inside, and also a strap wrench. Also given it a bit of a bang with a hammer, but nothing seems to work. Grateful for any suggestions. I've seen someone suggesting pouring boilling water over it, but will that damage the sealant around the bath? I really don't want to get into having to get someone to take the bath out (that's if I can find someone willing to do it).
Thanks

 

[Aquarius]

You could try the boiling water, shouldn’t damage the silicone. What grips you using?

 

[plomero]

Just normal grips, with the rubber from the strap wrench underneath to stop them damaging the chrome, although I there is already damage. I'm thinking that if I can't unscrew it, and if I can get a spare, then would the next thing be to get it off with a hacksaw or something?

 

[Aquarius]

If you can get a spare, then I’d try losing the rubber underneath, and apply a bit more pressure with the grips. Just a daft question, you are undoing the correct way? (Anti-clockwise).

 

[plomero]

If you can get a spare, then I’d try losing the rubber underneath, and apply a bit more pressure with the grips. Just a daft question, you are undoing the correct way? (Anti-clockwise).

Thanks. Yes, anticlockwise!

 

[SimonG]

If you can get a spare then use an old chisel and hammer to tap it round. Will bugger the piece but will come off.

 

[plomero]

If you can get a spare then use an old chisel and hammer to tap it round. Will bugger the piece but will come off.

Right, thanks. Should I pour boiling water with the handle off, to try to get it inside the cover?

 

[SimonG]

Right, thanks. Should I pour boiling water with the handle off, to try to get it inside the cover?

No need the chisel and hammer will do it.